10 ms·

DNS-Persist-01: A New Model for DNS-Based Challenge Validation

321 points by todsacerdoti 8mo ago

TrueDuality 8mo ago
I think this is solving a real operational pain point, definitely one that I've experienced. My biggest hesitation here is the direct exposure of the managing account identity not that I need to protect the accounts key material, I already need to do that. While "usernames" are not generally protected to the same degree as credentials, they do matter and act as an important gate to even know about before a real attack can commence. This also provides the ability to associate random found credentials back to the sites you can now issue certificates for if they're using the same account. This is free scope expansion for any breach that occurs. I guarantee sites like Shodan will start indexing these IDs on all domains they look at to provide those reverse lookup services.
- krunck 8mo ago
  Exactly. They should provide the user with a list of UUIDs(or any other randomish ID tied to the actual account) that can be used in the accounturi URL for these operations.
- gsich 8mo ago
  The account is the same as you create in any acme client. I don't see potential for a reverse lookup.
  - Ayesh 8mo ago
    I think the previous post is talking about a search that will find the sibling domain names that have obtained certificates with the same account ID. That is a strong indication that those domains are in the same certificate renewal pipeline, most likely on the same physical/virtual server.
    - mschuster91 8mo ago
      Run ACME inside a Docker container, one instance (and credentials) for each domain name. Doesn't consume much resources. The real problem is IP addresses anyway, CT logs "thankfully" feed information to every bad actor in real time, which makes data mining trivially easy.
      - cortesoft 8mo ago
        you dont even need a docker container to do that.
        mschuster91 8mo ago
        Agreed, that's just a personal preference thing of me. Harder to mess up and easier to route.
  - TrueDuality 8mo ago
    This is publicly publishing the account ID. There is an optional extension in RFC8659 that extends it but it isn't required by any implementer. This puts that ID into a public well known location that is easy to scrape and will be (this is exactly the kind of opsec info project like Maltego love to go lookup and pull in).
- liambigelow 8mo ago
  CAA records including an accounturi already expose the account identity in the same manner, so I feel like that ship has already sailed somewhat (and I would prefer that the CAA and persist record formats match).
  - Bender 8mo ago
    I think the difference is that using the existing DNS method listing the account is entirely optional. I have left it out on domains that I don't want correlated for that very reason.
  - TrueDuality 8mo ago
    The accounturi is an optional extension. Email, and phone are also optional. This is the first challenge that publicly requires you to specify your account ID publicly. There may be implementations that require it but neither Let's Encrypt or the protocols require them.
mmh0000 8mo ago
I really like and hate this at the same time. Years ago, I had a really fubar shell script for generating the DNS-01 records on my own (non-cloud) run authoritative nameserver. It "worked," but its reliability was highly questionable. I like this DNS-PERSIST fixes that. But I don't understand why they chose to include the account as a plain-text string in the DNS record. Seems they could have just as easily used a randomly generated key that wouldn't mean anything to anyone outside Let's Encrypt, and without exposing my account to every privacy-invasive bot and hacker.
- ragall 8mo ago
  Those who choose to use DNS-PERSIST-01 should fully commit to automation and create one LetsEncrypt account per FQDN (or at least per loadbalancer), using a UUID as username.
  - mcpherrinm 8mo ago
    There is no username in ACME besides the account URI, so the UUID you’re suggesting isn’t needed. The account uri themselves just have a number (db primary key). If you’re worried about correlating between domains, then yes just make multiple accounts. There is an email field in ACME account registration but we don’t persist that since we dropped sending expiry emails.
    - glzone1 8mo ago
      Interesting. I didn't realize the email field wasn't persisted. I assumed it could be used in some type of account recovery scenario.
    - 9dev 8mo ago
      It’s still a valid point IMHO - why not just use the public key directly? It seems like the account URI just adds problems instead of resolving any.
      - mcpherrinm 8mo ago
cyberax 8mo ago
Ah, the next step towards True DANE! We then can just staple the Persist DNS key to the certificate itself. And then we just need to cut out the middleman and add a new IETF standard for browsers to directly validate the certificates, as long as they confirm the DNS response using DNSSEC.
- tptacek 8mo ago
  This decreases the salience of DANE/DNSSEC by taking DNS queries off the per-issuance critical path. Attackers targeting multitenant platforms get only a small number of bites at the apple in this model.
  - cyberax 8mo ago
    Sure. It's yet another advantage of doing True DANE. But it still requires DNS to be reliable for the certificate issuance to work, there's no way around it. So why not cut out the middleman? (And the answer right now is "legacy compatibility")
    - tptacek 8mo ago
      I mean, the reason not to do DANE is that nobody will DNSSEC-sign, because DNSSEC signing is dangerous.
      - cyberax 8mo ago
        Come on. It's not dangerous, it's just inconvenient and clumsy. So nobody is really using it.
        akerl_ 8mo ago
        Ok, it's inconvenient and clumsy in ways that make it easy to shoot oneself in the foot. But that's not dangerous?
        8mo ago
micw 8mo ago
I wonder why they switched from a super-secure-super-complex (in terms of operations) way of doing DNS auth to a super-simple-no-cryptography-involved method that just relies on the account id. Why not using some public/private key auth where the dns contains a public key and the requesting server uses the private key to sign the cert request? This would decouple the authorization from the actual account. It would not reveal the account's identity. It could be used with multiple account (useful for a wildcard on the DNS plus several independent systems requesting certs for subdomains).
- tptacek 8mo ago
  The most common vector for DNS-based attacks on issuance is compromised registrar accounts, and no matter how complicated you make the cryptography, if you're layering it onto the DNS, those attacks will preempt the cryptography.
- Spivak 8mo ago
  Because LE keeps a mapping of account ids to emails and public keys. You have to have the private key to the ACME account to issue a cert. The cryptography is still there but the dance is done by certbot behind the scenes. Prior to this accounts were nearly pointless as proof of control was checked every time so people (rightfully) just threw away the account key LE generated for them. Now if you use PERSIST you have to keep it around and deploy it to servers you want to be able to issue certs.
- raquuk 8mo ago
  Using the account identifier in the record and and LE mapping the identifier to a public key internally enables key rotario without touching the record again.
newsoftheday 8mo ago
Today I do the following: /usr/bin/letsencrypt renew -n --agree-tos --email me@example.com --keep-until-expiring Will I need to change that? Will I need to manually add custom DNS entries to all my domains? PS To add, compared to dealing with some paid certificate services, LetsEncrypt has been a dream.
- dextercd 8mo ago
  This adds a new validation method that people can use if they want. The existing validation methods (https://letsencrypt.org/docs/challenge-types/ https://letsencrypt.org/docs/challenge-types/) aren't going away, so your current setup will keep working.
  - jsheard 8mo ago
    And to elaborate, the reasons you might want to use a DNS challenge are to acquire wildcard certificates, or to acquire regular certificates on a machine or domain which isn't directly internet-facing. If neither of those apply to you then the regular HTTP/TLS methods are fine.
    - newsoftheday 8mo ago
      OK I was sort of thinking that might be the case but wanted to make sure in case I had to start prepping now, thanks. We use no wildcard domains today, maybe down the road.
      - bombcar 8mo ago
        Wildcard domains are a great way to get certs for all your "internal systems" with only having to expose one (or a bit of one on DNS) to the Internet at large. This is going to greatly simplify some of my scripts.
  - newsoftheday 8mo ago
    This is good news, not sure I got that from reading the article but even if I had to do it, it wouldn't be the end of the world I guess.
Ayesh 8mo ago
I'm surprised the ballot passed, unanimously even! I get that storing the DNS credentials in the certificate renewal pipeline is risky, but many DNS providers have granular API access controls, so it is already possible to limit the surface area in case the keys get leaked. Plus, you can revoke the keys easily. The ACME account credentials are also accessible by the same renewal pipelines that has the DNS API credentials, so this does not provide any new isolation. ~It's also not quite clear how to revoke this challenge, and how domain expiration deal with this. The DNS record contents should have been at least the HMAC of the account key, the FQDN, and something that will invalidate if the domain is transferred somewhere else. The leaf DNSSEC key would have been perfect, but DNSSEC key rotation is also quite broken, so it wouldn't play nice.~ Is there a way to limit the challenge types with CAA records? You can limit it by an account number, and I believe that is the most tight control you have so far. --- Edit: thanks to the replies to this comment, I learned that this would provide invalidation simply by removing the DNS record, and that the DNS records are checked at renewal time with a much shorter validation TTL.
- amluto 8mo ago
  > but many DNS providers have granular API access controls And many providers don't. (Even big ones that are supposedly competent like Cloudflare.) And basically everyone who uses granular API keys are storing a cleartext key, which is no better and possibly worse than storing a credential for an ACME account.
- agwa 8mo ago
  > It's also not quite clear how to revoke this challenge, and how domain expiration deal with this CAs can cache the record lookup for no longer than 10 days. After 10 days, they have to check it again. If the record is gone, which would be expected if the domain has expired or been transferred, then the authorization is no longer valid. (I would have preferred a much shorter limit, like 8 hours, but 10 days is a lot better than the current 398 day limit for the original ACME DNS validation method.)
  - mcpherrinm 8mo ago
    We (Let’s Encrypt) also agree 10 days seems too long, so we are migrating to 7 hours, aligning with the restrictions on CAA records.
CqtGLRGcukpy 8mo ago
"Support for the draft specification is available now in Pebble, a miniature version of Boulder, our production CA software. Work is also in progress on a lego-cli client implementation to make it easier for subscribers to experiment with and adopt. Staging rollout is planned for late Q1 2026, with a production rollout targeted for some time in Q2 2026."
csense 8mo ago
To get a Let's Encrypt wildcard cert, I ended up running my own DNS server with dnsmasq and delegating the _acme-challenge subdomain to it. Pasting a challenge string once and letting its continued presence prove continued ownership of a domain is a great step forward. But I agree with others that there is absolutely no reason to expose account numbers; it should be a random ID associated with the account in Let's Encrypt's database. As a workaround, you should probably make a new account for each domain.
- Spivak 8mo ago
  You bothered to manage your LE accounts? I only say because when using the other two challenge types with most deployment scenarios you were generating a new account per cert so your account ID was just a string of random numbers.
- bombcar 8mo ago
  Your account ID is exposed in the certificate generated; what's the real difference?
  - pepdar 8mo ago
    The ACME account URI does not appear in issued certificates. X.509 certs contain the subject, issuer, SANs, validity period, SCTs, etc., but no ACME account identifier. You can verify this by inspecting any Let's Encrypt certificate. What CT logs do reveal is which CA issued certs for which domain(s), and multi-domain certs group SANs together, so some correlation is possible. But the account URI itself is not exposed — dns-persist-01 records in DNS would be a new exposure surface for that identifier. That's a real tradeoff, which is why the draft supports using separate accounts per domain if isolation matters to you.
Havoc 8mo ago
Interesting. Think a lot of the security headaches went away for me when I discovered providers like CF can restrict the scope of tokens to a single domain and lock it to my IP.
- amluto 8mo ago
  Even CF cannot restrict the scope of a token to a single host.
  - cube00 8mo ago
    Or a single DNS record.
jcalvinowens 8mo ago
Really happy to see this. In the meantime, if you use bind as your authoritative nameserver, you can limit an hmac-secret to one TXT record, so each webserver that uses rfc2136 for certificate renewals is only capable of updating its specific record: key "bob.acme." { algorithm hmac-sha512; secret "blahblahblah"; }; key "joe.acme." { algorithm hmac-sha512; secret "blahblahblah2"; }; zone "example.com" IN { type master; file "/var/lib/bind/example.com.zone"; update-policy { grant bob.acme. name _acme-challenge.bob.acme.example.com. TXT; grant joe.acme. name _acme-challenge.joe.acme.example.com. TXT; }; key-directory "/var/lib/bind/keys-acme.example.com"; dnssec-policy "acme"; inline-signing yes; }; I like this because it means an attacker who compromises "bob" can only get certs for "bob". The server part looks like this: export LE_CONFIG_HOME="/etc/acme-sh/" export NSUPDATE_SERVER="${YOUR_NS_ADDR}" export NSUPDATE_KEY="/var/lib/bob-nsupdate.key" export NSUPDATE_KEY_NAME="bob.acme." export NSUPDATE_ZONE="acme.example.com." acme.sh --issue --server letsencrypt -d 'bob.example.com' \ --certificate-profile shortlived \ --days 6 \ --dns dns_nsupdate
- xav0989 8mo ago
  If not using something like bind, but willing to run a dedicated dns server for acme challenges, acmedns offers something similar. When you generate a new account, it gets given a unique subdomain. You then cname the challenge domain to the acmedns subdomain and the account can only affect the associated subdomain.
ocdtrekkie 8mo ago
This might be the first time in ten years that a certificate proposal intends to make issuing certificates more reasonable and not less. More of this, less of 7-day-lifetime stupidity.
qwertox 8mo ago
This will make things so much easier. Here, certbot runs in Docker in the intranet, and on a VPS I have a custom-built nameserver to which all the _acme-challenge are redirected to via NS records. The system in the intranet starts certbot, makes it pass it the token-domain-pair from letsencrypt, it then sends those pairs to the nameserver which then attaches the token to a TXT record for that domain, so that the DNS reply can send this to letsencrypt when they request it. All that will be gone and I thank you for that! You add as much value to the internet as Wikipedia or OpenStreetMap.
itintheory 8mo ago
I'm really excited for this. We moved 120+ hand renewed certs to ACME, but still manually validate the domains annually. Many of them are on private/internal load balancers (no HTTP-01 challenge possible), and our DNS host doesn't support automation (no DNS-01 challenges either). While manually renewing the DCV for ~30 domains once a year isn't too bad, when the lifetime of that validity shrinks, ultimately to 9 days, it'd become a full time job. I just hope Sectigo implements this as quickly as LE.
- 9dev 8mo ago
  For the love of god, switch to a DNS provider with an API. Whatever legacy behemoth you’re working with doesn’t justify a gap this wide.
  - amluto 8mo ago
    Name one that doesn’t have an AWS-style per-query cost. (There might well be a nice one, but I haven’t found it yet.)
    - nfredericks 8mo ago
      Might be obvious, but Cloudflare
      - amluto 8mo ago
        No. Cloudflare will give a key scoped to an entire administrative domain in the Cloudflare sense like “a.com”. They will not give you a key scoped to a single entry within that domain. (That entry would be a domain in the RFC 9499 sense, but do you really expect anyone to agree on the terminology?) In particular, there is no support for getting a key scoped to _acme-challenge.a.b.c or, even better, to a particular RR. Maybe if you have an enterprise plan you can very awkwardly fudge it using lots of CNAMEs and subdomains. Some DNS hosts that support old-school dynamic dns can do this. dns.he.net is an example, but they have a login system that very much stuck in the nineties.
      - 8mo ago
bob1029 8mo ago
I've changed my mind about the short lived cert stuff after seeing what is enabled by IP address certificates with the HTTP-01 verification method. I don't even bother writing the cert to disk anymore. There is a background thread that checks to see if the current instance of the cert is null or older than 24h. The cert selector on aspnetcore just looks at this reference and blocks until its not null. Being able to distribute self-hostable software to users that can be deployed onto a VM and made operational literally within 5 minutes is a big selling point. Domain registration & DNS are a massive pain to deal with at the novice end of the spectrum. You can combine this with things like https://checkip.amazonaws.com https://checkip.amazonaws.com to build properly turnkey solutions.
- cube00 8mo ago
  Pretty risky given the rate limits of Let's Encrypt are non negotiable with no choice but to wait them out.
  - muvlon 8mo ago
    They are quite literally negotiable: https://isrg.formstack.com/forms/rate_limit_adjustment_request https://isrg.formstack.com/forms/rate_limit_adjustment_reque... There are also a bunch of rate limit exemptions that automatically apply whenever you "renew" a cert: https://letsencrypt.org/docs/rate-limits/#non-ari-renewals https://letsencrypt.org/docs/rate-limits/#non-ari-renewals. That means whenever you request a cert and there already is an issued certificate for the same set of identities.
    - dextercd 8mo ago
      Your comment is 100% correct, but I just want to point out that this doesn't negate the risks of bob's approach here. LE wouldn't see this as a legitimate reason to raise rate limits, and such a request takes weeks to handle anyway. Indeed, some rate limits don't apply for renewals but some still do.
    - cube00 8mo ago
      If you’ve hit a rate limit, we don’t have a way to temporarily reset it. [1] From your link move the adjustments to production twice monthly. I don't know about your use case but I couldn't risk being unable to get a new certificate for at least a fortnight because my container was stuck in a restart loop. [1]: https://letsencrypt.org/docs/rate-limits/ https://letsencrypt.org/docs/rate-limits/
chaz6 8mo ago
Is it possible to create an ACME account without requesting a certificate? AFAICT is is not so you cannot use this method unless you have first requested a certificate with some other method. I hope I am wrong!
- dextercd 8mo ago
  An account needs to be created before you can request a certificate. Some ACME clients might create the account for you implicitly when you request the first certificate, but in the background it still needs to start by registering an account. `certbot register` followed by `certbot show_account` is how you'd do this with certbot.
  - chaz6 8mo ago
    Great, thank you!
- plagiat0r 8mo ago
  Most acmev2 clients create account on certificate request. That is precisely why I wrote this: https://github.com/pawlakus/acmecli https://github.com/pawlakus/acmecli This small tool will allow you to just create, rekey and deactivate your acmev2 account(s).
aaomidi 8mo ago
This is significantly better than my draft of DNS-ACCOUNT-01. Thank you Let's Encrypt team!
zamadatix 8mo ago
Yeessss! This should finally make certificates for internal only web services actually easier to orchestrate than before ACME. This closes probably the biggest operational pain point I've had with letsencrypt/modern web certificates. Thank you so much to all inolved!
jmholla 8mo ago
There's a missing part here, and that's validating your ACME account ownership. I think most users depend on automation that creates their accounts, so they never have to deal with it. But now, you need to propagate some credential to validate your account ownership to the ACME provider. I would have liked to see some conversation about that in this announcement. I'm not familiar with Let's Encrypt's authentication model. If they don't have token creation that can be limited by target domain, but I expect you'll need to create separate accounts for each of your target domains, or else anything with that secret can create a cert for any domain your account controls.
- mschuster91 8mo ago
  > There's a missing part here, and that's validating your ACME account ownership. Why? ACME accounts have credentials so that the ACME client can authenticate against the certificate issuer, and ACME providers require the placement of a DNS record or a .well-known HTTP endpoint to verify that the account is authorized to act upon the demands of whoever owns the domain. If either your ACME credentials leak out or, even worse, someone manages to place DNS records or hijack your .well-known endpoint, you got far bigger problems at hand than someone being able to mis-issue SSL certificates under your domain name.
  - jmholla 8mo ago
    > Why? ACME accounts have credentials so that the ACME client can authenticate against the certificate issuer, and ACME providers require the placement of a DNS record or a .well-known HTTP endpoint to verify that the account is authorized to act upon the demands of whoever owns the domain. This is the previous models. In this case, DNS-Persist-01, the record is permanent and never changes. So to prove that your request is valid, they need to authenticate in some other manner. Otherwise, once you create that persistent record, anybody could request a cert for your domain. Edit: Spivak explains the flow differences better in their comment: https://news.ycombinator.com/item?id=47065821 https://news.ycombinator.com/item?id=47065821
basilikum 8mo ago
> The timestamp is expressed as UTC seconds since 1970-01-01 That should be TAI, right? Is that really correct or do they actually mean unix timestamps (those shift with leap seconds unlike TAI which is actually just the number of seconds that have passed since 1970001Z)?
- wtallis 8mo ago
  Do leap seconds even matter here? Doing anything involving DNS or certificates in a way that requires clock synchronization down to the second would seem to be asking for trouble.
  - toast0 8mo ago
    Probably yeah, seconds don't really matter here. You would have to work hard for the 27 second difference to be material. But precision is nice. unixtime is almost certainly what is meant by the standard, but it is not the count of UTC seconds since 1970; unix time is the number of seconds since 1970 as if all days had 86400 seconds. UTC, TAI, and GPS seconds are all the same length, and the same number have happened since 1970, but TAI appears 37 seconds ahead of UTC because TAI has days with 86400 seconds, while UTC has some days with 86401 seconds and was 10 seconds ahead of UTC in 1970. unixtime and UTC are in sync because unixtime allows some days to encompass 86401 UTC seconds while unixtime only counts 86400 seconds.
  - tialaramex 8mo ago
    Abolition of the Leap Second is basically a done deal. So, the differences caused by leap seconds will become frozen as arbitrary offsets, GPS time versus UTC for example. Basically when it was invented leap seconds seemed like a good idea because we assumed the inconvenience versus value was a good trade, but in practice we've discovered the value is negligible and the inconvenience more than we expected, so, bye bye leap seconds. The body responsible has formal treaty promises to make UTC track the Earth's spin and replacing those treaties is a huge pain, so, the "hack" proposed is to imagine into existence a leap minute or even a leap hour that could correct for the spin, and then in practice those will never be used either because it's even less convenient than a leap second - but by the time they're asked to set a date for these hypothetical changes likely the signatory countries won't exist and their successors can just sign a revised treaty, countries only tend to last a few hundred years, look at the poor US which is preparing 250th anniversary celebrations while also approaching civil war.
mscdex 8mo ago
After having to deal with VM hosts that do GeoIP blocking, which unintentionally blocks Let's Encrypt and others from properly verifying domains via http-01/tls-alpn-01, I settled on a DIY solution that uses CNAME redirects and a custom, minimal DNS server for handling the redirected dns-01 challenges. It's essentially a greatly simplified version of the acme-dns project tailored to my project's needs (and written in node.js instead of Go). Unfortunately with dns-persist-01 including account information in the DNS record itself, that's a bit of a show stopper for me. If/when account information changes, that means DNS records need changing and getting clients to update their DNS records (for any reason) has long been a pain.
- pepdar 8mo ago
  Key rotation doesn't change the account URI — ACME key rollover (RFC 8555 §7.3.5) replaces the key pair but keeps the same account URL, which is one of the reasons the draft uses account URI rather than a public key. Your DNS record stays unchanged through key rotations. The only case that requires a DNS update is creating an entirely new account, and that's deliberate — the record binds a specific account to the domain so a stolen record can't be used by someone else. For your setup with CNAME delegation to a custom DNS server, this should actually be simpler than dns-01. You would point _validation-persist instead of _acme-challenge, and the target record is static. No per-issuance dynamic updates at all.
Ajedi32 8mo ago
This is going to make it way easier to get publicly trusted certs for LAN servers that aren't internet facing. I'm looking forward to every admin UI out there being able to generate a string you can just paste into a DNS record to instantly get a Let's Encrypt cert.
- kami23 8mo ago
  Just experienced this with my heavily networked off openclaw setup. I gave up and will do manual renewals until I have more time to figure out a good way of doing it. I was trying to get a cert for some headscale magic dns setups, but I think that's way more complicated than I thought it would be.
kittbuilds 8mo ago
[dead]
infogulch 8mo ago
This is a nice increment in ACME usability. Once again I would like to ask CA/B to permit name constrained, short lifespan, automatically issued intermediate CAs. Last year's request: https://news.ycombinator.com/item?id=43563676 https://news.ycombinator.com/item?id=43563676
IgorPartola 8mo ago
Am I just stupidly missing something or does this in theory allow anyone who controls a DNS server for my domain or anyone who controls traffic between LE and the DNS server for my domain to get a TLS certificate they can use to impersonate my domain? I suppose the same is true for DNS-01 but this would make it even easier because the attacker can just put up their LE account instead of mine into the DNS response and get a certificate. At this point why not just put my public cert into a DNS record and be done with it?
- bombcar 8mo ago
  Yes, anyone who controls your DNS can get a TLS certificate from anyone who offers them - because, uh, they control your DNS! Try to figure out a way to block me from getting a TLS certificate if I can modify your DNS.
  - IgorPartola 8mo ago
    That’s fair but I also have to trust every provider between my DNS server and LE’s servers to not intercept DNS responses. Since DNS isn’t encrypted anyone anywhere between them can modify the traffic and get a certificate if I understand correctly.
    - mcpherrinm 8mo ago
      Two current mitigations and one future: DNSSEC prevents any modification of records, but isn’t widely deployed. We query authoritative nameservers directly from at least four places, over a diverse set of network connections, from multiple parts of the world. This (called MPIC) makes interception more difficult. We are also working on DNS over secure transports to authoritative nameservers, for cases where DNSSEC isn’t or won’t be deployed.
      - IgorPartola 8mo ago
        Ah that makes sense. I was wondering why I haven’t heard of cases of successfully attacks like this. Thank you for the info!
CaliforniaKarl 8mo ago
For folks who use certbot, here is where they are tracking work on support for this feature: https://github.com/certbot/certbot/issues/10549 https://github.com/certbot/certbot/issues/10549
dangoodmanUT 8mo ago
Love this, such a better method
1vuio0pswjnm7 8mo ago
Is it false that DNS requests sent from LE to authoritatuve nameservers are unencrypted
- 1vuio0pswjnm7 8mo ago
  Answer: "Yes, standard DNS queries are unencrypted. The threat model relies on MPIC - querying from multiple vantage points - not transport encryption. DNSSEC adds an integrity layer where available." https://news.ycombinator.com/item?id=47073054 https://news.ycombinator.com/item?id=47073054
rmoriz 8mo ago
I would have loved to see mandatory DNSSEC requirements
gerdesj 8mo ago
My LE experience (post HTTP-01 and now DNS-01) - its a bit of a palava. I don't have to open port 80 which is nice for ... security audits but gains zero security benefit. I have a PowerDNS server running locally with a static IPv4 address via NAT and I have created a DNS domain and enabled dynamic DNS updates from certain IPv4 addresses with a pre-shared key. For each cert you need a DNS CNAME pointing to my DNS domain in a specific format. Then we have to get to grips with software to do the deed. acme.sh is superb for !Windows. simple-acme is fine for Windows. I still setup each one by hand instead of ansible/Zenworks/whatever because I'm a sucker for punishment and still small enough for now. DNS-Persist-01 is not something I think I will ever need but clearly someone does.
tripdout 8mo ago
For local services, I don't see the benefit of using DNS challenges and a Let's Encrypt certificate over running my own CA and generating my own certificates. It's not that much work to trust my root certificate on each device, and then I don't need an internet connection to verify local service certificates.
- sebiw 8mo ago
  > It's not that much work to trust my root certificate on each device Sure, but is trusting your homebrewed CA on all your devices for essentially everything really a good idea? When your homebrewed CA somehow gets compromised, all your devices are effectively compromised and not only for local connections, but everything that uses PKIX.
  - NewJazz 8mo ago
    Name constraints https://systemoverlord.com/2020/06/14/private-ca-with-x-509-name-constraints.html https://systemoverlord.com/2020/06/14/private-ca-with-x-509-...
    - 8organicbits 8mo ago
      Make sure all the TLS clients you use have support for name constraints. When I evaluated this in 2023, Chrome was in the process of adding support. I'd love to see a caniuse style analysis of TLS features, people assume they work but support varies.
- Hamuko 8mo ago
  I can either add a Cloudflare API key and Certbot on my NAS, or I could generate a root certificate and add it to my desktop computers, laptop, tablet, phones, Apple TV, etc. Doesn't seem that tough of a choice. I guess in the future I could even forego the Cloudflare API key and just have the persistent DNS record there once.
blahgeek 8mo ago
Given the name of DNS-01, you would think it would be called DNS-02...
solatic 8mo ago
I'm surprised that this doesn't require DNSSEC or at the very least actively encourage configuring DNSSEC. While I used to be fully in the camp that DNSSEC was way more trouble than it was worth, in particular when access was de-facto secured by trusted CA certificates, more and more DNS record types (CAA, CERT, SSHFP, these TXT records) are responsible for storing information that can be manipulated in MITM attacks to seize control of a root of trust. Of course, this has little applicability to anyone who is small enough not to have nation-state level actors in their threat model. But when I look behind the curtain of even Fortune 100 companies that really ought to have nation-state level actors in their threat model, too often you find people who are just not operating at that level or are swamped with unrelated work. So I'm starting to become of the opinion that guidance should change here and at the very least be documented recommendations - if it's not encouraged down the organizational size scale, too often it's not applied further up where it's needed.
- ajnin 8mo ago
  DNSSEC is encouraged ("SHOULD" wording) in the RFC draft : https://datatracker.ietf.org/doc/html/draft-ietf-acme-dns-persist-00#name-dnssec https://datatracker.ietf.org/doc/html/draft-ietf-acme-dns-pe...
  - solatic 8mo ago
    The RFC wording is a little weird. If the zone has DNSSEC configured, then the wording should be stronger and use MUST wording, and not imply that CAs will be compliant if they choose to avoid verifying signatures despite the presence of signstures. Likewise, these TXT records for dns-persist-01 ideally "SHOULD NOT" be deployed when DNSSEC is not configured.
    - pepdar 8mo ago
      An open PR on the draft (#35) adds exactly this language: if a CA performs DNSSEC validation and it fails (expired signatures, broken chain of trust), the CA MUST treat it as a challenge failure and MUST NOT use the record. The rationale is that dns-persist-01 records are long-lived, so a DNSSEC failure has more severe consequences than it would for a transient challenge.
pepdar 8mo ago
I'm one of the draft authors. Several questions here touch real design tradeoffs — addressing the main threads: Why account URI instead of a public key in the record? (micw, 9dev, csense) Three reasons: 1. Key rotation without DNS changes. dns-persist-01 exists because DNS updates are expensive. Embedding a public key forces a DNS update on every key rotation — the exact problem this method solves. The account URI survives key rotation (RFC 8555 §7.3.5). 2. CAA alignment. The accounturi parameter matches CAA record syntax (RFC 8657 §3). Domain owners use the same identifier in validation and policy records. 3. Simplicity. Matching uses simple string comparison — no key encoding, no signature verification, no algorithm negotiation. The cryptographic binding between account URI and key pair happens inside ACME, where it belongs. "Exposing account numbers" / privacy (csense, mmh0000, bflesch) The account URI is opaque — a URL containing a database key, like https://acme-v02.api.letsencrypt.org/acme/acct/123456789 https://acme-v02.api.letsencrypt.org/acme/acct/123456789. No email, no name. The privacy exposure is modest: it reveals which CA account controls the domain, similar to what CT logs already show about CA-domain relationships, but with explicit account-level grouping. If you want isolation between domains, use separate accounts. The accounturi binds validation to a specific account so a stolen DNS record can't be used by a different subscriber. An open PR (#35) adds accounturi to the challenge object so clients can verify it before provisioning. 10-day reuse limit (agwa) The 10-day maximum comes from the CA/Browser Forum ballot (SC-088), not the IETF draft. The draft defers reuse period to CA policy and caps it at the DNS TTL (see "Validation Data Reuse and TTL Handling" in the Security Considerations). Let's Encrypt is migrating to 7 hours. The TTL cap lets domain owners enforce shorter windows directly. Mandatory DNSSEC (rmoriz) Requiring DNSSEC would exclude most domains and block adoption. The current draft specifies DNSSEC validation as SHOULD. An open PR (#35) tightens this: if a CA performs DNSSEC validation and it fails — expired signatures, broken chain of trust — the CA MUST reject the record. This is stricter than general ACME guidance because dns-persist-01 records are long-lived. MPIC (multi-perspective validation) provides the primary defense against on-path attacks regardless of DNSSEC. Unencrypted DNS queries (1vuio0pswjnm7) Yes, standard DNS queries are unencrypted. The threat model relies on MPIC — querying from multiple vantage points — not transport encryption. DNSSEC adds an integrity layer where available. CAA interaction (Ayesh) Yes. A CAA record with validationmethods=dns-persist-01 combined with accounturi restricts who can validate using this method. Name-constrained intermediate CAs (infogulch) Separate problem. dns-persist-01 reduces operational cost of leaf cert issuance by eliminating per-issuance DNS interaction. Delegated intermediates shift the trust model. Both could coexist. Draft: <https://github.com/ietf-wg-acme/draft-ietf-acme-dns-persist https://github.com/ietf-wg-acme/draft-ietf-acme-dns-persist> (PR #35 is an open pull request on the draft with several of the improvements mentioned above.)
stego-tech 8mo ago
This is a blessing for us Dynamic DNS folks whose DNS providers demand a static IP for changes to come from (i.e., Namecheap). In theory, it means we can set this up once (or on a schedule that works for our needs), and trust that renewals will happen without continued maintenance or involvement. Eager to give this a try as I modernize the homelab.

321 points by todsacerdoti 8mo ago

I think this is solving a real operational pain point, definitely one that I've experienced. My biggest hesitation here is the direct exposure of the managing account identity not that I need to protect the accounts key material, I already need to do that. While "usernames" are not generally protected to the same degree as credentials, they do matter and act as an important gate to even know about before a real attack can commence. This also provides the ability to associate random found credentials back to the sites you can now issue certificates for if they're using the same account. This is free scope expansion for any breach that occurs. I guarantee sites like Shodan will start indexing these IDs on all domains they look at to provide those reverse lookup services.

krunck 8mo ago
Exactly. They should provide the user with a list of UUIDs(or any other randomish ID tied to the actual account) that can be used in the accounturi URL for these operations.
gsich 8mo ago
The account is the same as you create in any acme client. I don't see potential for a reverse lookup.
- Ayesh 8mo ago
  I think the previous post is talking about a search that will find the sibling domain names that have obtained certificates with the same account ID. That is a strong indication that those domains are in the same certificate renewal pipeline, most likely on the same physical/virtual server.
  - mschuster91 8mo ago
    Run ACME inside a Docker container, one instance (and credentials) for each domain name. Doesn't consume much resources. The real problem is IP addresses anyway, CT logs "thankfully" feed information to every bad actor in real time, which makes data mining trivially easy.
    - cortesoft 8mo ago
      you dont even need a docker container to do that.
      - mschuster91 8mo ago
        Agreed, that's just a personal preference thing of me. Harder to mess up and easier to route.
- TrueDuality 8mo ago
  This is publicly publishing the account ID. There is an optional extension in RFC8659 that extends it but it isn't required by any implementer. This puts that ID into a public well known location that is easy to scrape and will be (this is exactly the kind of opsec info project like Maltego love to go lookup and pull in).
liambigelow 8mo ago
CAA records including an accounturi already expose the account identity in the same manner, so I feel like that ship has already sailed somewhat (and I would prefer that the CAA and persist record formats match).
- Bender 8mo ago
  I think the difference is that using the existing DNS method listing the account is entirely optional. I have left it out on domains that I don't want correlated for that very reason.
- TrueDuality 8mo ago
  The accounturi is an optional extension. Email, and phone are also optional. This is the first challenge that publicly requires you to specify your account ID publicly. There may be implementations that require it but neither Let's Encrypt or the protocols require them.

mmh0000 8mo ago

I really like and hate this at the same time. Years ago, I had a really fubar shell script for generating the DNS-01 records on my own (non-cloud) run authoritative nameserver. It "worked," but its reliability was highly questionable. I like this DNS-PERSIST fixes that. But I don't understand why they chose to include the account as a plain-text string in the DNS record. Seems they could have just as easily used a randomly generated key that wouldn't mean anything to anyone outside Let's Encrypt, and without exposing my account to every privacy-invasive bot and hacker.

ragall 8mo ago
Those who choose to use DNS-PERSIST-01 should fully commit to automation and create one LetsEncrypt account per FQDN (or at least per loadbalancer), using a UUID as username.
- mcpherrinm 8mo ago
  There is no username in ACME besides the account URI, so the UUID you’re suggesting isn’t needed. The account uri themselves just have a number (db primary key). If you’re worried about correlating between domains, then yes just make multiple accounts. There is an email field in ACME account registration but we don’t persist that since we dropped sending expiry emails.
  - glzone1 8mo ago
    Interesting. I didn't realize the email field wasn't persisted. I assumed it could be used in some type of account recovery scenario.
  - 9dev 8mo ago
    It’s still a valid point IMHO - why not just use the public key directly? It seems like the account URI just adds problems instead of resolving any.
    - mcpherrinm 8mo ago

cyberax 8mo ago

Ah, the next step towards True DANE! We then can just staple the Persist DNS key to the certificate itself. And then we just need to cut out the middleman and add a new IETF standard for browsers to directly validate the certificates, as long as they confirm the DNS response using DNSSEC.

tptacek 8mo ago
This decreases the salience of DANE/DNSSEC by taking DNS queries off the per-issuance critical path. Attackers targeting multitenant platforms get only a small number of bites at the apple in this model.
- cyberax 8mo ago
  Sure. It's yet another advantage of doing True DANE. But it still requires DNS to be reliable for the certificate issuance to work, there's no way around it. So why not cut out the middleman? (And the answer right now is "legacy compatibility")
  - tptacek 8mo ago
    I mean, the reason not to do DANE is that nobody will DNSSEC-sign, because DNSSEC signing is dangerous.
    - cyberax 8mo ago
      Come on. It's not dangerous, it's just inconvenient and clumsy. So nobody is really using it.
      - akerl_ 8mo ago
        Ok, it's inconvenient and clumsy in ways that make it easy to shoot oneself in the foot. But that's not dangerous?
        8mo ago

micw 8mo ago

I wonder why they switched from a super-secure-super-complex (in terms of operations) way of doing DNS auth to a super-simple-no-cryptography-involved method that just relies on the account id. Why not using some public/private key auth where the dns contains a public key and the requesting server uses the private key to sign the cert request? This would decouple the authorization from the actual account. It would not reveal the account's identity. It could be used with multiple account (useful for a wildcard on the DNS plus several independent systems requesting certs for subdomains).

tptacek 8mo ago
The most common vector for DNS-based attacks on issuance is compromised registrar accounts, and no matter how complicated you make the cryptography, if you're layering it onto the DNS, those attacks will preempt the cryptography.
Spivak 8mo ago
Because LE keeps a mapping of account ids to emails and public keys. You have to have the private key to the ACME account to issue a cert. The cryptography is still there but the dance is done by certbot behind the scenes. Prior to this accounts were nearly pointless as proof of control was checked every time so people (rightfully) just threw away the account key LE generated for them. Now if you use PERSIST you have to keep it around and deploy it to servers you want to be able to issue certs.
raquuk 8mo ago
Using the account identifier in the record and and LE mapping the identifier to a public key internally enables key rotario without touching the record again.

newsoftheday 8mo ago

Today I do the following: /usr/bin/letsencrypt renew -n --agree-tos --email me@example.com --keep-until-expiring Will I need to change that? Will I need to manually add custom DNS entries to all my domains? PS To add, compared to dealing with some paid certificate services, LetsEncrypt has been a dream.

dextercd 8mo ago
This adds a new validation method that people can use if they want. The existing validation methods (https://letsencrypt.org/docs/challenge-types/ https://letsencrypt.org/docs/challenge-types/) aren't going away, so your current setup will keep working.
- jsheard 8mo ago
  And to elaborate, the reasons you might want to use a DNS challenge are to acquire wildcard certificates, or to acquire regular certificates on a machine or domain which isn't directly internet-facing. If neither of those apply to you then the regular HTTP/TLS methods are fine.
  - newsoftheday 8mo ago
    OK I was sort of thinking that might be the case but wanted to make sure in case I had to start prepping now, thanks. We use no wildcard domains today, maybe down the road.
    - bombcar 8mo ago
      Wildcard domains are a great way to get certs for all your "internal systems" with only having to expose one (or a bit of one on DNS) to the Internet at large. This is going to greatly simplify some of my scripts.
- newsoftheday 8mo ago
  This is good news, not sure I got that from reading the article but even if I had to do it, it wouldn't be the end of the world I guess.

Ayesh 8mo ago

I'm surprised the ballot passed, unanimously even! I get that storing the DNS credentials in the certificate renewal pipeline is risky, but many DNS providers have granular API access controls, so it is already possible to limit the surface area in case the keys get leaked. Plus, you can revoke the keys easily. The ACME account credentials are also accessible by the same renewal pipelines that has the DNS API credentials, so this does not provide any new isolation. ~It's also not quite clear how to revoke this challenge, and how domain expiration deal with this. The DNS record contents should have been at least the HMAC of the account key, the FQDN, and something that will invalidate if the domain is transferred somewhere else. The leaf DNSSEC key would have been perfect, but DNSSEC key rotation is also quite broken, so it wouldn't play nice.~ Is there a way to limit the challenge types with CAA records? You can limit it by an account number, and I believe that is the most tight control you have so far. --- Edit: thanks to the replies to this comment, I learned that this would provide invalidation simply by removing the DNS record, and that the DNS records are checked at renewal time with a much shorter validation TTL.

amluto 8mo ago
> but many DNS providers have granular API access controls And many providers don't. (Even big ones that are supposedly competent like Cloudflare.) And basically everyone who uses granular API keys are storing a cleartext key, which is no better and possibly worse than storing a credential for an ACME account.
agwa 8mo ago
> It's also not quite clear how to revoke this challenge, and how domain expiration deal with this CAs can cache the record lookup for no longer than 10 days. After 10 days, they have to check it again. If the record is gone, which would be expected if the domain has expired or been transferred, then the authorization is no longer valid. (I would have preferred a much shorter limit, like 8 hours, but 10 days is a lot better than the current 398 day limit for the original ACME DNS validation method.)
- mcpherrinm 8mo ago
  We (Let’s Encrypt) also agree 10 days seems too long, so we are migrating to 7 hours, aligning with the restrictions on CAA records.

CqtGLRGcukpy 8mo ago

"Support for the draft specification is available now in Pebble, a miniature version of Boulder, our production CA software. Work is also in progress on a lego-cli client implementation to make it easier for subscribers to experiment with and adopt. Staging rollout is planned for late Q1 2026, with a production rollout targeted for some time in Q2 2026."

csense 8mo ago

To get a Let's Encrypt wildcard cert, I ended up running my own DNS server with dnsmasq and delegating the _acme-challenge subdomain to it. Pasting a challenge string once and letting its continued presence prove continued ownership of a domain is a great step forward. But I agree with others that there is absolutely no reason to expose account numbers; it should be a random ID associated with the account in Let's Encrypt's database. As a workaround, you should probably make a new account for each domain.

Spivak 8mo ago
You bothered to manage your LE accounts? I only say because when using the other two challenge types with most deployment scenarios you were generating a new account per cert so your account ID was just a string of random numbers.
bombcar 8mo ago
Your account ID is exposed in the certificate generated; what's the real difference?
- pepdar 8mo ago
  The ACME account URI does not appear in issued certificates. X.509 certs contain the subject, issuer, SANs, validity period, SCTs, etc., but no ACME account identifier. You can verify this by inspecting any Let's Encrypt certificate. What CT logs do reveal is which CA issued certs for which domain(s), and multi-domain certs group SANs together, so some correlation is possible. But the account URI itself is not exposed — dns-persist-01 records in DNS would be a new exposure surface for that identifier. That's a real tradeoff, which is why the draft supports using separate accounts per domain if isolation matters to you.

Havoc 8mo ago

Interesting. Think a lot of the security headaches went away for me when I discovered providers like CF can restrict the scope of tokens to a single domain and lock it to my IP.

amluto 8mo ago
Even CF cannot restrict the scope of a token to a single host.
- cube00 8mo ago
  Or a single DNS record.

jcalvinowens 8mo ago

Really happy to see this. In the meantime, if you use bind as your authoritative nameserver, you can limit an hmac-secret to one TXT record, so each webserver that uses rfc2136 for certificate renewals is only capable of updating its specific record: key "bob.acme." { algorithm hmac-sha512; secret "blahblahblah"; }; key "joe.acme." { algorithm hmac-sha512; secret "blahblahblah2"; }; zone "example.com" IN { type master; file "/var/lib/bind/example.com.zone"; update-policy { grant bob.acme. name _acme-challenge.bob.acme.example.com. TXT; grant joe.acme. name _acme-challenge.joe.acme.example.com. TXT; }; key-directory "/var/lib/bind/keys-acme.example.com"; dnssec-policy "acme"; inline-signing yes; }; I like this because it means an attacker who compromises "bob" can only get certs for "bob". The server part looks like this: export LE_CONFIG_HOME="/etc/acme-sh/" export NSUPDATE_SERVER="${YOUR_NS_ADDR}" export NSUPDATE_KEY="/var/lib/bob-nsupdate.key" export NSUPDATE_KEY_NAME="bob.acme." export NSUPDATE_ZONE="acme.example.com." acme.sh --issue --server letsencrypt -d 'bob.example.com' \ --certificate-profile shortlived \ --days 6 \ --dns dns_nsupdate

xav0989 8mo ago
If not using something like bind, but willing to run a dedicated dns server for acme challenges, acmedns offers something similar. When you generate a new account, it gets given a unique subdomain. You then cname the challenge domain to the acmedns subdomain and the account can only affect the associated subdomain.

ocdtrekkie 8mo ago

This might be the first time in ten years that a certificate proposal intends to make issuing certificates more reasonable and not less. More of this, less of 7-day-lifetime stupidity.

qwertox 8mo ago

This will make things so much easier. Here, certbot runs in Docker in the intranet, and on a VPS I have a custom-built nameserver to which all the _acme-challenge are redirected to via NS records. The system in the intranet starts certbot, makes it pass it the token-domain-pair from letsencrypt, it then sends those pairs to the nameserver which then attaches the token to a TXT record for that domain, so that the DNS reply can send this to letsencrypt when they request it. All that will be gone and I thank you for that! You add as much value to the internet as Wikipedia or OpenStreetMap.

itintheory 8mo ago

I'm really excited for this. We moved 120+ hand renewed certs to ACME, but still manually validate the domains annually. Many of them are on private/internal load balancers (no HTTP-01 challenge possible), and our DNS host doesn't support automation (no DNS-01 challenges either). While manually renewing the DCV for ~30 domains once a year isn't too bad, when the lifetime of that validity shrinks, ultimately to 9 days, it'd become a full time job. I just hope Sectigo implements this as quickly as LE.

9dev 8mo ago
For the love of god, switch to a DNS provider with an API. Whatever legacy behemoth you’re working with doesn’t justify a gap this wide.
- amluto 8mo ago
  Name one that doesn’t have an AWS-style per-query cost. (There might well be a nice one, but I haven’t found it yet.)
  - nfredericks 8mo ago
    Might be obvious, but Cloudflare
    - amluto 8mo ago
      No. Cloudflare will give a key scoped to an entire administrative domain in the Cloudflare sense like “a.com”. They will not give you a key scoped to a single entry within that domain. (That entry would be a domain in the RFC 9499 sense, but do you really expect anyone to agree on the terminology?) In particular, there is no support for getting a key scoped to _acme-challenge.a.b.c or, even better, to a particular RR. Maybe if you have an enterprise plan you can very awkwardly fudge it using lots of CNAMEs and subdomains. Some DNS hosts that support old-school dynamic dns can do this. dns.he.net is an example, but they have a login system that very much stuck in the nineties.
    - 8mo ago

bob1029 8mo ago

I've changed my mind about the short lived cert stuff after seeing what is enabled by IP address certificates with the HTTP-01 verification method. I don't even bother writing the cert to disk anymore. There is a background thread that checks to see if the current instance of the cert is null or older than 24h. The cert selector on aspnetcore just looks at this reference and blocks until its not null. Being able to distribute self-hostable software to users that can be deployed onto a VM and made operational literally within 5 minutes is a big selling point. Domain registration & DNS are a massive pain to deal with at the novice end of the spectrum. You can combine this with things like https://checkip.amazonaws.com https://checkip.amazonaws.com to build properly turnkey solutions.

cube00 8mo ago
Pretty risky given the rate limits of Let's Encrypt are non negotiable with no choice but to wait them out.
- muvlon 8mo ago
  They are quite literally negotiable: https://isrg.formstack.com/forms/rate_limit_adjustment_request https://isrg.formstack.com/forms/rate_limit_adjustment_reque... There are also a bunch of rate limit exemptions that automatically apply whenever you "renew" a cert: https://letsencrypt.org/docs/rate-limits/#non-ari-renewals https://letsencrypt.org/docs/rate-limits/#non-ari-renewals. That means whenever you request a cert and there already is an issued certificate for the same set of identities.
  - dextercd 8mo ago
    Your comment is 100% correct, but I just want to point out that this doesn't negate the risks of bob's approach here. LE wouldn't see this as a legitimate reason to raise rate limits, and such a request takes weeks to handle anyway. Indeed, some rate limits don't apply for renewals but some still do.
  - cube00 8mo ago
    If you’ve hit a rate limit, we don’t have a way to temporarily reset it. [1] From your link move the adjustments to production twice monthly. I don't know about your use case but I couldn't risk being unable to get a new certificate for at least a fortnight because my container was stuck in a restart loop. [1]: https://letsencrypt.org/docs/rate-limits/ https://letsencrypt.org/docs/rate-limits/

chaz6 8mo ago

Is it possible to create an ACME account without requesting a certificate? AFAICT is is not so you cannot use this method unless you have first requested a certificate with some other method. I hope I am wrong!

dextercd 8mo ago
An account needs to be created before you can request a certificate. Some ACME clients might create the account for you implicitly when you request the first certificate, but in the background it still needs to start by registering an account. `certbot register` followed by `certbot show_account` is how you'd do this with certbot.
- chaz6 8mo ago
  Great, thank you!
plagiat0r 8mo ago
Most acmev2 clients create account on certificate request. That is precisely why I wrote this: https://github.com/pawlakus/acmecli https://github.com/pawlakus/acmecli This small tool will allow you to just create, rekey and deactivate your acmev2 account(s).

aaomidi 8mo ago

This is significantly better than my draft of DNS-ACCOUNT-01. Thank you Let's Encrypt team!

zamadatix 8mo ago

Yeessss! This should finally make certificates for internal only web services actually easier to orchestrate than before ACME. This closes probably the biggest operational pain point I've had with letsencrypt/modern web certificates. Thank you so much to all inolved!

jmholla 8mo ago

There's a missing part here, and that's validating your ACME account ownership. I think most users depend on automation that creates their accounts, so they never have to deal with it. But now, you need to propagate some credential to validate your account ownership to the ACME provider. I would have liked to see some conversation about that in this announcement. I'm not familiar with Let's Encrypt's authentication model. If they don't have token creation that can be limited by target domain, but I expect you'll need to create separate accounts for each of your target domains, or else anything with that secret can create a cert for any domain your account controls.

mschuster91 8mo ago
> There's a missing part here, and that's validating your ACME account ownership. Why? ACME accounts have credentials so that the ACME client can authenticate against the certificate issuer, and ACME providers require the placement of a DNS record or a .well-known HTTP endpoint to verify that the account is authorized to act upon the demands of whoever owns the domain. If either your ACME credentials leak out or, even worse, someone manages to place DNS records or hijack your .well-known endpoint, you got far bigger problems at hand than someone being able to mis-issue SSL certificates under your domain name.
- jmholla 8mo ago
  > Why? ACME accounts have credentials so that the ACME client can authenticate against the certificate issuer, and ACME providers require the placement of a DNS record or a .well-known HTTP endpoint to verify that the account is authorized to act upon the demands of whoever owns the domain. This is the previous models. In this case, DNS-Persist-01, the record is permanent and never changes. So to prove that your request is valid, they need to authenticate in some other manner. Otherwise, once you create that persistent record, anybody could request a cert for your domain. Edit: Spivak explains the flow differences better in their comment: https://news.ycombinator.com/item?id=47065821 https://news.ycombinator.com/item?id=47065821

basilikum 8mo ago

> The timestamp is expressed as UTC seconds since 1970-01-01 That should be TAI, right? Is that really correct or do they actually mean unix timestamps (those shift with leap seconds unlike TAI which is actually just the number of seconds that have passed since 1970001Z)?

wtallis 8mo ago
Do leap seconds even matter here? Doing anything involving DNS or certificates in a way that requires clock synchronization down to the second would seem to be asking for trouble.
- toast0 8mo ago
  Probably yeah, seconds don't really matter here. You would have to work hard for the 27 second difference to be material. But precision is nice. unixtime is almost certainly what is meant by the standard, but it is not the count of UTC seconds since 1970; unix time is the number of seconds since 1970 as if all days had 86400 seconds. UTC, TAI, and GPS seconds are all the same length, and the same number have happened since 1970, but TAI appears 37 seconds ahead of UTC because TAI has days with 86400 seconds, while UTC has some days with 86401 seconds and was 10 seconds ahead of UTC in 1970. unixtime and UTC are in sync because unixtime allows some days to encompass 86401 UTC seconds while unixtime only counts 86400 seconds.
- tialaramex 8mo ago
  Abolition of the Leap Second is basically a done deal. So, the differences caused by leap seconds will become frozen as arbitrary offsets, GPS time versus UTC for example. Basically when it was invented leap seconds seemed like a good idea because we assumed the inconvenience versus value was a good trade, but in practice we've discovered the value is negligible and the inconvenience more than we expected, so, bye bye leap seconds. The body responsible has formal treaty promises to make UTC track the Earth's spin and replacing those treaties is a huge pain, so, the "hack" proposed is to imagine into existence a leap minute or even a leap hour that could correct for the spin, and then in practice those will never be used either because it's even less convenient than a leap second - but by the time they're asked to set a date for these hypothetical changes likely the signatory countries won't exist and their successors can just sign a revised treaty, countries only tend to last a few hundred years, look at the poor US which is preparing 250th anniversary celebrations while also approaching civil war.

mscdex 8mo ago

After having to deal with VM hosts that do GeoIP blocking, which unintentionally blocks Let's Encrypt and others from properly verifying domains via http-01/tls-alpn-01, I settled on a DIY solution that uses CNAME redirects and a custom, minimal DNS server for handling the redirected dns-01 challenges. It's essentially a greatly simplified version of the acme-dns project tailored to my project's needs (and written in node.js instead of Go). Unfortunately with dns-persist-01 including account information in the DNS record itself, that's a bit of a show stopper for me. If/when account information changes, that means DNS records need changing and getting clients to update their DNS records (for any reason) has long been a pain.

pepdar 8mo ago
Key rotation doesn't change the account URI — ACME key rollover (RFC 8555 §7.3.5) replaces the key pair but keeps the same account URL, which is one of the reasons the draft uses account URI rather than a public key. Your DNS record stays unchanged through key rotations. The only case that requires a DNS update is creating an entirely new account, and that's deliberate — the record binds a specific account to the domain so a stolen record can't be used by someone else. For your setup with CNAME delegation to a custom DNS server, this should actually be simpler than dns-01. You would point _validation-persist instead of _acme-challenge, and the target record is static. No per-issuance dynamic updates at all.

Ajedi32 8mo ago

This is going to make it way easier to get publicly trusted certs for LAN servers that aren't internet facing. I'm looking forward to every admin UI out there being able to generate a string you can just paste into a DNS record to instantly get a Let's Encrypt cert.

kami23 8mo ago
Just experienced this with my heavily networked off openclaw setup. I gave up and will do manual renewals until I have more time to figure out a good way of doing it. I was trying to get a cert for some headscale magic dns setups, but I think that's way more complicated than I thought it would be.

kittbuilds 8mo ago

[dead]

infogulch 8mo ago

This is a nice increment in ACME usability. Once again I would like to ask CA/B to permit name constrained, short lifespan, automatically issued intermediate CAs. Last year's request: https://news.ycombinator.com/item?id=43563676 https://news.ycombinator.com/item?id=43563676

IgorPartola 8mo ago

Am I just stupidly missing something or does this in theory allow anyone who controls a DNS server for my domain or anyone who controls traffic between LE and the DNS server for my domain to get a TLS certificate they can use to impersonate my domain? I suppose the same is true for DNS-01 but this would make it even easier because the attacker can just put up their LE account instead of mine into the DNS response and get a certificate. At this point why not just put my public cert into a DNS record and be done with it?

bombcar 8mo ago
Yes, anyone who controls your DNS can get a TLS certificate from anyone who offers them - because, uh, they control your DNS! Try to figure out a way to block me from getting a TLS certificate if I can modify your DNS.
- IgorPartola 8mo ago
  That’s fair but I also have to trust every provider between my DNS server and LE’s servers to not intercept DNS responses. Since DNS isn’t encrypted anyone anywhere between them can modify the traffic and get a certificate if I understand correctly.
  - mcpherrinm 8mo ago
    Two current mitigations and one future: DNSSEC prevents any modification of records, but isn’t widely deployed. We query authoritative nameservers directly from at least four places, over a diverse set of network connections, from multiple parts of the world. This (called MPIC) makes interception more difficult. We are also working on DNS over secure transports to authoritative nameservers, for cases where DNSSEC isn’t or won’t be deployed.
    - IgorPartola 8mo ago
      Ah that makes sense. I was wondering why I haven’t heard of cases of successfully attacks like this. Thank you for the info!

CaliforniaKarl 8mo ago

For folks who use certbot, here is where they are tracking work on support for this feature: https://github.com/certbot/certbot/issues/10549 https://github.com/certbot/certbot/issues/10549

dangoodmanUT 8mo ago

Love this, such a better method

1vuio0pswjnm7 8mo ago

Is it false that DNS requests sent from LE to authoritatuve nameservers are unencrypted

1vuio0pswjnm7 8mo ago
Answer: "Yes, standard DNS queries are unencrypted. The threat model relies on MPIC - querying from multiple vantage points - not transport encryption. DNSSEC adds an integrity layer where available." https://news.ycombinator.com/item?id=47073054 https://news.ycombinator.com/item?id=47073054

rmoriz 8mo ago

I would have loved to see mandatory DNSSEC requirements

gerdesj 8mo ago

My LE experience (post HTTP-01 and now DNS-01) - its a bit of a palava. I don't have to open port 80 which is nice for ... security audits but gains zero security benefit. I have a PowerDNS server running locally with a static IPv4 address via NAT and I have created a DNS domain and enabled dynamic DNS updates from certain IPv4 addresses with a pre-shared key. For each cert you need a DNS CNAME pointing to my DNS domain in a specific format. Then we have to get to grips with software to do the deed. acme.sh is superb for !Windows. simple-acme is fine for Windows. I still setup each one by hand instead of ansible/Zenworks/whatever because I'm a sucker for punishment and still small enough for now. DNS-Persist-01 is not something I think I will ever need but clearly someone does.

tripdout 8mo ago

For local services, I don't see the benefit of using DNS challenges and a Let's Encrypt certificate over running my own CA and generating my own certificates. It's not that much work to trust my root certificate on each device, and then I don't need an internet connection to verify local service certificates.

sebiw 8mo ago
> It's not that much work to trust my root certificate on each device Sure, but is trusting your homebrewed CA on all your devices for essentially everything really a good idea? When your homebrewed CA somehow gets compromised, all your devices are effectively compromised and not only for local connections, but everything that uses PKIX.
- NewJazz 8mo ago
  Name constraints https://systemoverlord.com/2020/06/14/private-ca-with-x-509-name-constraints.html https://systemoverlord.com/2020/06/14/private-ca-with-x-509-...
  - 8organicbits 8mo ago
    Make sure all the TLS clients you use have support for name constraints. When I evaluated this in 2023, Chrome was in the process of adding support. I'd love to see a caniuse style analysis of TLS features, people assume they work but support varies.
Hamuko 8mo ago
I can either add a Cloudflare API key and Certbot on my NAS, or I could generate a root certificate and add it to my desktop computers, laptop, tablet, phones, Apple TV, etc. Doesn't seem that tough of a choice. I guess in the future I could even forego the Cloudflare API key and just have the persistent DNS record there once.

blahgeek 8mo ago

Given the name of DNS-01, you would think it would be called DNS-02...

solatic 8mo ago

I'm surprised that this doesn't require DNSSEC or at the very least actively encourage configuring DNSSEC. While I used to be fully in the camp that DNSSEC was way more trouble than it was worth, in particular when access was de-facto secured by trusted CA certificates, more and more DNS record types (CAA, CERT, SSHFP, these TXT records) are responsible for storing information that can be manipulated in MITM attacks to seize control of a root of trust. Of course, this has little applicability to anyone who is small enough not to have nation-state level actors in their threat model. But when I look behind the curtain of even Fortune 100 companies that really ought to have nation-state level actors in their threat model, too often you find people who are just not operating at that level or are swamped with unrelated work. So I'm starting to become of the opinion that guidance should change here and at the very least be documented recommendations - if it's not encouraged down the organizational size scale, too often it's not applied further up where it's needed.

ajnin 8mo ago
DNSSEC is encouraged ("SHOULD" wording) in the RFC draft : https://datatracker.ietf.org/doc/html/draft-ietf-acme-dns-persist-00#name-dnssec https://datatracker.ietf.org/doc/html/draft-ietf-acme-dns-pe...
- solatic 8mo ago
  The RFC wording is a little weird. If the zone has DNSSEC configured, then the wording should be stronger and use MUST wording, and not imply that CAs will be compliant if they choose to avoid verifying signatures despite the presence of signstures. Likewise, these TXT records for dns-persist-01 ideally "SHOULD NOT" be deployed when DNSSEC is not configured.
  - pepdar 8mo ago
    An open PR on the draft (#35) adds exactly this language: if a CA performs DNSSEC validation and it fails (expired signatures, broken chain of trust), the CA MUST treat it as a challenge failure and MUST NOT use the record. The rationale is that dns-persist-01 records are long-lived, so a DNSSEC failure has more severe consequences than it would for a transient challenge.

pepdar 8mo ago

I'm one of the draft authors. Several questions here touch real design tradeoffs — addressing the main threads: Why account URI instead of a public key in the record? (micw, 9dev, csense) Three reasons: 1. Key rotation without DNS changes. dns-persist-01 exists because DNS updates are expensive. Embedding a public key forces a DNS update on every key rotation — the exact problem this method solves. The account URI survives key rotation (RFC 8555 §7.3.5). 2. CAA alignment. The accounturi parameter matches CAA record syntax (RFC 8657 §3). Domain owners use the same identifier in validation and policy records. 3. Simplicity. Matching uses simple string comparison — no key encoding, no signature verification, no algorithm negotiation. The cryptographic binding between account URI and key pair happens inside ACME, where it belongs. "Exposing account numbers" / privacy (csense, mmh0000, bflesch) The account URI is opaque — a URL containing a database key, like https://acme-v02.api.letsencrypt.org/acme/acct/123456789 https://acme-v02.api.letsencrypt.org/acme/acct/123456789. No email, no name. The privacy exposure is modest: it reveals which CA account controls the domain, similar to what CT logs already show about CA-domain relationships, but with explicit account-level grouping. If you want isolation between domains, use separate accounts. The accounturi binds validation to a specific account so a stolen DNS record can't be used by a different subscriber. An open PR (#35) adds accounturi to the challenge object so clients can verify it before provisioning. 10-day reuse limit (agwa) The 10-day maximum comes from the CA/Browser Forum ballot (SC-088), not the IETF draft. The draft defers reuse period to CA policy and caps it at the DNS TTL (see "Validation Data Reuse and TTL Handling" in the Security Considerations). Let's Encrypt is migrating to 7 hours. The TTL cap lets domain owners enforce shorter windows directly. Mandatory DNSSEC (rmoriz) Requiring DNSSEC would exclude most domains and block adoption. The current draft specifies DNSSEC validation as SHOULD. An open PR (#35) tightens this: if a CA performs DNSSEC validation and it fails — expired signatures, broken chain of trust — the CA MUST reject the record. This is stricter than general ACME guidance because dns-persist-01 records are long-lived. MPIC (multi-perspective validation) provides the primary defense against on-path attacks regardless of DNSSEC. Unencrypted DNS queries (1vuio0pswjnm7) Yes, standard DNS queries are unencrypted. The threat model relies on MPIC — querying from multiple vantage points — not transport encryption. DNSSEC adds an integrity layer where available. CAA interaction (Ayesh) Yes. A CAA record with validationmethods=dns-persist-01 combined with accounturi restricts who can validate using this method. Name-constrained intermediate CAs (infogulch) Separate problem. dns-persist-01 reduces operational cost of leaf cert issuance by eliminating per-issuance DNS interaction. Delegated intermediates shift the trust model. Both could coexist. Draft: <https://github.com/ietf-wg-acme/draft-ietf-acme-dns-persist https://github.com/ietf-wg-acme/draft-ietf-acme-dns-persist> (PR #35 is an open pull request on the draft with several of the improvements mentioned above.)

stego-tech 8mo ago

This is a blessing for us Dynamic DNS folks whose DNS providers demand a static IP for changes to come from (i.e., Namecheap). In theory, it means we can set this up once (or on a schedule that works for our needs), and trust that renewals will happen without continued maintenance or involvement. Eager to give this a try as I modernize the homelab.