4 ms·

I'd be curious whether there's any security concerns on this one. Could an attacker craft a message that gets access to execute commands into a client terminal?

freedomben 2y ago
Yeah, though SSH is already very mature at processing text, so it's a surprisingly good fit for a chat. I would also remember that any machine you SSH from is going to give the server some metadata like IP address, public keys (which aren't useful as creds but can be for tracking). Really fun little project though
- tjoff 2y ago
  SSH might be, but maybe not your terminal. Which the very least can possibly trick you using escape codes. Also, unless my memory fails me 'cat'ing an untrusted file isn't recommended for security reasons. Additionally you should disable SSH forwarding. Relevant thread from the startup selling coffee over SSH: https://news.ycombinator.com/item?id=40227624 https://news.ycombinator.com/item?id=40227624
qudat 2y ago
This is not sshd, this is a golang binary that uses the stdlib ssh lib. You would have to either a) figure out how to escape out of a golang binary, or b) if the go code executes shell commands with some user provided text, trying to shell inject something in there.
- cwillu 2y ago
  Or convince the ssh daemon to pass on terminal escape codes to another user. https://nvd.nist.gov/vuln/detail/CVE-2021-33477 https://nvd.nist.gov/vuln/detail/CVE-2021-33477
  - deleted 2y ago
    [deleted]
  - quackduck 2y ago
    whoa
  - raggi 2y ago
    yup, not an extensive list, but further demonstrative: - terminal emulators are not security hardened clients against malicious actors - ssh lacks PKI and is inconvenient so users never do prekeying in practice, so it's TOFU / zero server assertion in most practical cases (i.e. easy to mitm) - ssh channel features are a constant concern, for server resources and for client features like agents, agents are easy to disable - most ssh implementations don't scale that well, it wasn't ever really a goal to do so - there are few tools for auditing and monitoring, unlike the common protocols/services/clients fun for toys, but i wouldn't put credit card details in there, unlike some streamers started doing lately.
    - cwillu 2y ago
      ssh definitely supports PKI, it's just not the standard workflow for individuals ssh-keygen (1): ssh-keygen supports signing of keys to produce certificates that may be used for user or host authentication. Certificates consist of a public key, some identity information, zero or more principal (user or host) names and a set of options that are signed by a Certification Authority (CA) key. Clients or servers may then trust only the CA key and verify its signature on a certificate rather than trusting many user/host keys. Note that OpenSSH certificates are a different, and much simpler, format to the X.509 certificates used in ssl(8)
      - raggi 2y ago
        I'm not talking about supporting public key cryptography, I'm talking about having a specific and usable deployment of a PKI. The closest thing SSH has is SSHFP, which depends on DNSSEC, which is according to many opinions, DOA.
      - 2y ago
phoyd 2y ago
I'm also interested. Setting up a passwordless SSH account for some public service sounds like a good way to give your machine away to North Korean hackers, because you forgot to set someting in /etc/sshd to "no". Is there a usable description somewhere on how to do this safely?
- quackduck 2y ago
  i'd be interested in seeing that. here its ok because it doesnt use sshd at all
  - queuebert 2y ago
    So it's using a new stack that hasn't been vetted like OpenSSH? I'd rather use OpenSSH + LibreSSL for this application.
- fragmede 2y ago
  https://news.ycombinator.com/item?id=41002245 https://news.ycombinator.com/item?id=41002245
Tepix 2y ago
You may not want the chat server owner to know which public ssh key you are using for privacy reasons. Workaround: Specify another ssh keypair

freedomben 2y ago

Yeah, though SSH is already very mature at processing text, so it's a surprisingly good fit for a chat. I would also remember that any machine you SSH from is going to give the server some metadata like IP address, public keys (which aren't useful as creds but can be for tracking). Really fun little project though

tjoff 2y ago
SSH might be, but maybe not your terminal. Which the very least can possibly trick you using escape codes. Also, unless my memory fails me 'cat'ing an untrusted file isn't recommended for security reasons. Additionally you should disable SSH forwarding. Relevant thread from the startup selling coffee over SSH: https://news.ycombinator.com/item?id=40227624 https://news.ycombinator.com/item?id=40227624

qudat 2y ago

This is not sshd, this is a golang binary that uses the stdlib ssh lib. You would have to either a) figure out how to escape out of a golang binary, or b) if the go code executes shell commands with some user provided text, trying to shell inject something in there.

cwillu 2y ago
Or convince the ssh daemon to pass on terminal escape codes to another user. https://nvd.nist.gov/vuln/detail/CVE-2021-33477 https://nvd.nist.gov/vuln/detail/CVE-2021-33477
- deleted 2y ago
  [deleted]
- quackduck 2y ago
  whoa
- raggi 2y ago
  yup, not an extensive list, but further demonstrative: - terminal emulators are not security hardened clients against malicious actors - ssh lacks PKI and is inconvenient so users never do prekeying in practice, so it's TOFU / zero server assertion in most practical cases (i.e. easy to mitm) - ssh channel features are a constant concern, for server resources and for client features like agents, agents are easy to disable - most ssh implementations don't scale that well, it wasn't ever really a goal to do so - there are few tools for auditing and monitoring, unlike the common protocols/services/clients fun for toys, but i wouldn't put credit card details in there, unlike some streamers started doing lately.
  - cwillu 2y ago
    ssh definitely supports PKI, it's just not the standard workflow for individuals ssh-keygen (1): ssh-keygen supports signing of keys to produce certificates that may be used for user or host authentication. Certificates consist of a public key, some identity information, zero or more principal (user or host) names and a set of options that are signed by a Certification Authority (CA) key. Clients or servers may then trust only the CA key and verify its signature on a certificate rather than trusting many user/host keys. Note that OpenSSH certificates are a different, and much simpler, format to the X.509 certificates used in ssl(8)
    - raggi 2y ago
      I'm not talking about supporting public key cryptography, I'm talking about having a specific and usable deployment of a PKI. The closest thing SSH has is SSHFP, which depends on DNSSEC, which is according to many opinions, DOA.
    - 2y ago

phoyd 2y ago

I'm also interested. Setting up a passwordless SSH account for some public service sounds like a good way to give your machine away to North Korean hackers, because you forgot to set someting in /etc/sshd to "no". Is there a usable description somewhere on how to do this safely?

quackduck 2y ago
i'd be interested in seeing that. here its ok because it doesnt use sshd at all
- queuebert 2y ago
  So it's using a new stack that hasn't been vetted like OpenSSH? I'd rather use OpenSSH + LibreSSL for this application.
fragmede 2y ago
https://news.ycombinator.com/item?id=41002245 https://news.ycombinator.com/item?id=41002245

Tepix 2y ago

You may not want the chat server owner to know which public ssh key you are using for privacy reasons. Workaround: Specify another ssh keypair