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It's possible to forge headers in certain circumstances. It's not easy. And this is the first time this has happened. It's ridiculously easy to forge email hea
by jcnnghm 16y ago
It's possible to forge headers in certain circumstances. It's not easy. And this is the first time this has happened.
It's ridiculously easy to forge email headers. Headers are manually created whenever programmatically sending email messages. That's how messages can be sent from addresses that don't exist, like devnull@example.com or noreply@yourdomain.com. They don't even send a confirmation email that you have to approve before stuff is posted?
- kwyjibo 16y agoNo, they don't.
- edanm 16y agoAs I understand it, they send you a mail telling you about the post and letting you remove it. Not perfect, but probably works 99% of the time.
- loewenskind 16y ago99% of the time? So if someone decides to trash my reputation they can just post a bunch of stupid blog entries as me and it is on me to (a) detect that this even happened by checking my mail, (b) go do whatever work needed to remove the post and (c) try to explain to everyone what happened (likely causing even more people to do it when they realize how ridiculous the system I'm using is) and salvage my reputation? That doesn't sound like "works 99% of the time" to me, that sounds like an epic fail. EDIT: It appears that this was more of a configuration issue, so the above only applies if you set up your account this way.
- edanm 16y agoClarification: by 99%, I meant it works for 99% of users, whom no one will ever try and attack. Obviously it's just my opinion.
- isleyaardvark 16y agoYou can already post a bunch of stupid blog comments as someone else, as long as people realize Posterous has a similar problem, it's not going to ruin your life. (Plus, (a) doesn't seem to be that big of a problem for a service you're using your email to access.)
- macrael 16y agoCommenting on someone's site using a different name is pretty different from being able to fake a post. I have no expectation that comments are written by who they say they are, but I do expect all the posts to be written by the same person.
- leftnode 16y agoShouldn't it work oppositely? Prevent the post from appearing until you explicitly approve it from a link in an email.
- megamark16 16y agoYes, and unless I'm missing something I don't see a way to turn this type of confirmation-before-posting functionality on.
- k33n 16y agoSort of defeats the purpose of Posterous though. It's nice to be able to send an email and be done with it. Though for an account coming under constant attack, it'd be nice to have the option though. Edit: What they should really do is obfuscate the posting email addresses a little. Make my posting email 1234randomwords@posterous.com, and give me the option to change it to something else if I am coming under attack.
- dimarco 16y agoI don't think it defeats the purpose, so to speak, since it's verified by another email. You never have to leave your email client. It's certainly and extra step that takes away from the smooth flowing process already set in place, though.
- jcnnghm 16y agoHeaders are manually created whenever programmatically sending email messages To clarify this a little, in case anyone isn't familiar, to send an email message programmatically, you basically just send a string with some headers and body content to the email server. Here are what the headers look like: Date: Sat, 13 Jun 2009 06:53:06 -0400 From: Mail Delivery Subsystem <MAILER-DAEMON> Message-Id: <200906131053.n5DAr2Nv025105@jclinux> To: <root@jclinux> To change the sender, all you'd need to do is change the from line. For example: From: Steve Jobs <sjobs@apple.com> A default sendmail implementation will deliver that message all day. Email headers should never be used for authentication.
- robinduckett 16y agoThat was my point. When I read in his article that he wasn't requiring a password to post, I thought I'd see if he was telling the truth, turns out he was.
- adamsmith 16y agoBut most major domains use domain keys / DKIM. http://en.wikipedia.org/wiki/DKIM http://en.wikipedia.org/wiki/DKIM As far as I understand it, you can't fake being an SMTP server sending mail from such a domain because their emails get signed with a private key whose matching public key is published by DNS.
- geocar 16y agoThere are several ways to defeat DKIM here: • If you can break DNS, you can get an NXDOMAIN reply, making recipients think there aren't any domainkeys • If the domainkey private key is small, you can factor it. There's an article on HN's frontpage right now about this. • If the server uses domainkeys, but it doesn't specifically verify the From: header, an attacker can still forge a message if they share a popular mail provider with their target. I don't know if this is still practical. • Stupidity. DKIM is difficult to test, and as a security measure it would need to be tested. An autoreponse confirmation would be immune to all of these attacks and would be trivial to implement correctly.
- borisk 16y agoHeaders are name/value pairs, a typical email will have 20 of those. It's possible to copy them if you have received an email from the blog owner or maybe from a mailing list post.
- crc5002 16y agoYou only need to know the owner's email address. Access to a message or a mailing list post by them won't provide any further advantage.
- borisk 16y agoEmail address is not enough. This one case was a coincidence. "We had a specific problem with the way we dealt with SPF records. Dustin didn't set any up, and there was a specific way that Robin Duckett's email server responded that caused us to flag it as a false negative for spoofing."
- crc5002 16y agoI think he said that: The blog owner's email host did not provide SPF protection; the intruder's email host appended some headers that lured Posterous to classify the email as genuine. So, having access to the blog owner's email headers would not have provided any additional advantage to the intruder.
- dcurtis 16y agoI updated the post to reflect reality. Usually, Posterous catches this stuff and sends an email asking you to confirm that you really are you. They analyze the headers more closely than just looking at the name. For some reason, this didn't work in this case.
- coderdude 16y agoAccording to him he just changed his email address to your email address in Outlook. Edit: dcurtis edited his comment. Originally he claimed there was some kind of secret algorithm that prevents spoofing.
- deleted 16y ago[deleted]
- loup-vaillant 16y agoBut, if they only analyse the headers, they are screwed anyway. Don't they also check the IP of the SMTP server as well or something?
- ergo98 16y agoI honestly am at a loss to understand how Dustin Curtis keeps getting linked from here.