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CERT: Sendmail Distribution Contained Trojan Horse
Scoria writes "According to a CERT advisory published this afternoon, the public distribution of Sendmail 8.12.6 contained a trojan horse from September 28 to October 6. For more detailed information, please consult advisory CA-2002-28." This sounds very much like what happened to OpenSSH.
As long as you could also get the source to the Trojan, as well... right?
Many eyes = better security but only when many > 0
...and that's why you should actually use those MD5 checksums, instead of unpacking and installing without thinking.
PGP signing is a good way to prevent trojaned software like this case. But I think the process to verify the software is too complicated and not easy for all users to use. Let me ask you this, when is the last time you checked the hash or PGP signature after you download a software?
For most people, never.... It would be great if we have automatic download tools to check signature as well (obviously, we need standard for storing the signature as well)
This is a good reason to compare the MD5 checksum of anything you download, source or binary, to what the author says it should be, especially if you downloaded from a mirror. Better yet, the author could use GnuPG and sign the code with his/her private key. Since only his/her public key can decrypt it, you know that the code has very likely not been tampered with.
bytesmythe
Hypocrisy is the resin that holds the plywood of society together.
-- Scott Meyer
It's been a long time since I installed sendmail or inn or bind from sources. At some point I stopped checking MD5 signatures, and now I trust the major distros to do that for me. I sure hope they're more vigilant than me. And I used to be so paranoid... This is a nasty wake-up call.
everyone says just check sums, but how are these people changing the file? If they can change the tarball on the server than why not change the page to have thier md5?
What?! It's not M$? oh.......
Good thing I use Exchange Server. I've got a tight ship there.
That way when you get your software you know who put the security holes in it. It's all part of trustworthy computing... ;-)
According to the advisory, it was only the FTP site that was compromised (The HTTP was fine).
So, as for those that are saying it's an Open Source problem, this is just wrong.
There's been alot more closed software distributed with Viri/Trojan Horses. The truth is, this is bound to happen if the public archives are on an unsecured server...I even seem to remember pressed CDs being distributed with trojans.
So, what are they doing to keep this from happening again?
Is doing a
# netstat -a | grep 6667
all that is necessary to see if one has a the open port, or is there more to it than that?
After reading the posting we'll note this is VERY similar to the OpenSSH trojan. The trojan doesn't wind up in the sendmail binary but is actually created during the build process.
So more than just checking the MD5sums of things you download you need to watch who you compile as, since the trojan will have the privledges of whoever compiled sendmail. This isn't exactly the most sly trojan either, it is quite blatent about how it creates a tunnel to a specified target, this can also help the intruder avoid firewall rules and detection.
If you find you've been affected by the trojan you would be wise to reinstall the system from known clean code since the intruder may have already created other backdoors from themself.
Ahem. Sorry. Couldn't resist. AAH! Don't mark it troll yet! Keep reading!
Ok, folks will say "Well here's a great example of a problem cryptography would prevent." Well as long as the guys inserting the trojans aren't contributing to your code base. Minor detail there. Keep in mind that a "trojan" can be as easy to code up as allowing a buffer overflow to take place (AND you have plausible deniability there.) Ok. So I'm paranoid.
So lets talk about the crypto side of things again. Since I'm paranoid and all that. Do you trust the project maintainer's system security? Reckon he allows anyone to log into his system? Do you trust their security and the network they come over? For that matter, reckon the CVS archive the code's stored on could be compromised? Do you see what we're up against yet? Paranoia...
Ok, lets say we've checked out his sytem and it's sterling. Key server/key management is a big pain in the ass right now. It'd be nice to have some infrastructure in place where I could go to a brick and mortar, establish my identity (Here's my passport, driver's license yadda yadda) and load MY PGP public key onto their server with their signature attached. Might even be worth a few bucks for me. That'd make that whole expiration thing pretty easy to deal with too.
It also seems to be that the US Postal Service would be the ideal venue for this infrastructure. As much of a pain in the ass as they are to deal with, it'd make the whole key revocation/renewal thing much easier. And it'd be a whole lot more secure than me asking my friends to sign my key via E-mail.
I'm trying to teach myself to set people on fire with my mind... Is it hot in here?
While sendmail is much more secure now, in the days of yore it made IIS look like fort knox.
Let's see, a Trojan Horse is basically defined as an undocumented chunk of code hiding inside a program, which does something that you don't know about or understand.
Sendmail is such a complex beast that, no matter how much you personally know about it, there are always things in there that you don't know about or understand.
So it has always been full or Trojan Horses.
This is the fundamental thing that's wrong with building a hugs program that tries to do everything possible. Pretty much all the other mail tools are better at sendmail in this respect, because they only try to be a mail tool.
Sendmail, OTOH, is an emulator for a rather complex sort of machine language. Some time back, someone demonstrated that it was possible to emulate a Turing machine with a sendmail.cf file. Impressive as this may be technically, it's way overkill for the task, and it shouldn't be any surprise to anyone when problems turn up in sendmail and aren't discoverted for a while.
It's guaranteed that there are others lurking inside that monster.
Those who do study history are doomed to stand helplessly by while everyone else repeats it.
How 'bout a quick tutorial from someone who knows pgp or gpg or MD5 on how to use it to figure out if my recent install is trojaned?
Also, the CERT advisory doesn't give any fixes, it just gives the signatures. It doesn't seem like installing a good version would eliminate the trojan.
It seems like every time a new trojan/worm/misc virus hits the scene, a thousand posts go up accusing that software of being horribly insecure and advocating some other software of the same type as being better.
It's quite simple... software can be infected by viruses, open source, closed source, any operating system or language. Just because today it's Sendmail that took a hit doesn't mean that it couldn't be qmail tomorrow.
If you got a virus, don't blame it on the software you downloaded, blame it on yourself for not validating it first.
By reading this comment, you immediately waive any and all rights regarding it.
Yes, of course, that was exactly what I meant. Thank goodness you were on the ball, or someone would have thought that I was alluding to Fort Knox's traditional reputation of extremely high security.
Yup, I got slimed, and I'm not an easy person to slime. This dude is the first person ever to get one up on me. But I'll have my revenge. I diffed the malicious source tree with the authentic one and found the malicious code. It looks amazingly innocuous until you base64 decode the shell script :-). His IP address is 66.37.138.99.
>It is still funny, simply because it is yet
>another sendmail problem.
Yeah, and if someone breaks into your house and pees on your carpet, it's yet another carpet problem.
Matt
>After the number of open e-mail relays I've had to
>deal with, sendmail leaves a sour taste in my
>mouth.
Sendmail hasn't allowed relaying at all for about five years unless you explicitely turn it on. In otherwords, blame site admins, not Sendmail.
Matt
MD5 Checksums have a higher rate of collisions, both in the wild and artifically. A machine can be built for only around $100k or less which can find collisions in less than 24 hours. Hell, in a few years standard computers could probably generate collisions easily. SHA1 (Simple Hash Algorithm) is a much better alternative over MD5.
The previous version of MD5, MD4, was so flawed it is now considered "broken". "Dobbertin [Dob95] has shown how collisions for the full version of MD4 can be found in under a minute on a typical PC... Clearly, MD4 should now be considered broken.".
SHA1, while of the same family of hashes as MD4 and MD5, remains uncompromised by any research discoveries, and is widely used in many applications requiring the highest levels of security.
Gnutella, the File Sharing Protocol, uses SHA1 over MD5 for the same reasons I state here. A developer of Bitzi (the Metadata/Hash catalog) has also recommended to the Gnutella Developer Forum not to use MD5, but SHA1 instead. Thus, people should be using SHA1 instead of MD5. I've noticed some major websites and companies are using MD5 hash's now, such as Adobe and Roxio. I would recommend to them to change them to SHA1 instead, since Gnutella supports it (and the fact that it is a much more secure and stronger hash algorithm)... and they can use MAGNET URI's to link to the files on Gnutella.
(sorry, I have to get this out of my system)
...
:-)
READ THE ARTICLE AND REALIZE WHAT IS GOING ON!
It says that:
The FTP-server of sendmail.org was compromised.
It doesn't say that:
- somebody commited code to the CVS server.
- nobody reads the commitlog of the CVS server.
It says that:
The sendmail-distribution was trojaned.
It doesn't say that:
- sendmail itself was trojaned
- there are trojans inside sendmail
- qmail/postfix is better because it isn't trojaned.
- exchange is better because the source is closed. It's the distribution which is corrupted, not the software.
It says that:
The correct MD5-checksum is
It doesn't say that:
- with PGP signing it wouldn't be prevented. Security is a process, you need to follow the rules or you are not secure. You should check all checksum/signatures you have, preferable from independant resources (e.g. one from sendmail.com and one from your unix-distribution).
Next time, please read the article and realize what's going on before you post (apologies to the people who actually did
Edwin (yes, the guy from the OpenSSH trojan)
bash$
-f
www.blackant.net
I have made the backdoor'd sendmail code available at http://www.enzotech.net/files/sm.backdoor.patch and the base64 portion is decoded at http://www.enzotech.net/files/sm.backdoor.base64.t xt
This was diff'd from a previously downloaded tar ball that we were using for analysis of another bug.
Bill Stewart
New Fast-Compression-only CPR http://preview.tinyurl.com/dy575ks
I think sendmail.org should up the version number at once and kill the .6 version once and for all. That would allow many people to look at what they have and say "yep, its .6, throw it out" but they want to keep the old version number so people get to play games. There are many reasons why they won't have the origianl tar ball and they have a very simple way to insure people don't have the trojaned version.
I download the tarball and MD5s. Then I want to verify the signature. For that I need a public key or something like that of the developer that signed the tarball.Since I never met him, I must resort to download also that from an internet place, probably the same from which I downloaded the source.
Now, what prevents whoever cracked the server and placed the troianed tarballs on it, to also change the public key, so that it matches the couterfeit signed tarball?
At a minimum, one should go to some forum/ML and check the key with a dozen or so other users, choosing the ones that got the key in different places and times.
Or am I missing something ?
Ciao
----
FB
If files from ftp.sendmail.org get infected, then people could probably get a bogus key as well.
This difference, though, is that one can download a public GPG key from a site (like sendmail.org or something) and continue using it to verify software over several versions.
Not only that, but public keys (or even complete keyrings containing public keys for groups of developers) can be obtained from multiple, different sources, all of which in turn are different and ideally independent of where one downloads the source tarball from.
This means one can obtain a developer's key or keyring from, say, a public key server (or two, or several), some ftp site (preferably a different non-mirror one from the tarball), a purchased CD, or any number of other places, check them against each other (make sure none disagree), and use them to check a download immediately, as well as 5 years from now.
The cracker would have to not only trojan the tarball, but also break into numerous independent key servers around the globe, numerous ftp sites around the globe, likely numerous web sites as well, and perhaps even various freenet nodes as well (if that is being used to distribute keys as well). And for those who anti up $5 for a CD with developers keys on it, they'd have to intercept the postal service and swap CDs as well (or crack the master CD before it goes to press).
Good luck. Even the NSA would probably have trouble pulling something like that off.
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