HT to @wdormann here - somebody has backdoored the open source project XZ which has downstream impacts.
For example, although OpenSSH doesn’t use XZ, Debian patch OpenSSH and introduced a dependency which translates as the XZ changes introducing a sshd authentication bypass backdoor it appears.
One dude bothered to investigate in his free time about why ssh was running slow, so it was caught fairly early - i.e. hopefully before distros started bundling it.
As I said, the impact here will be very limited due to how quick it was caught. Everybody owes the finder a beer.
NOTE: THIS IS AN ATTEMPT AT INCLUDING A BACKDOOR. THIS IS LEFT FOR HISTORICAL PURPOSES ONLY AND MUST NOT BE DONE. Please sync xz-utils 5.6.1-1 (main) from Debian unstable (main) Hello! I am one of the upstream maintainers for XZ Utils. Version 5.6.1 was recently released and uploaded to Debian as a bugfix only release. Notably, this fixes a bug that causes Valgrind to issue a warning on any application dynamically linked with liblzma. This includes a lot of important applications. This cou...
Originally reported on Google Code with ID 342 What steps will reproduce the problem? 1. Testcase is attached. Compile with GCC with -fsanitize=address option. 2. Run. 3. What is the expected outpu...
Back in 2022 a host of characters appeared and basically bullied the creator of the XZ project to hand it over to somebody else - at the time the guy cited mental health issues around not updating the project quickly.
At the time he was already talking about maybe handing over to the account who years later introduced the backdoor.
In mid 2023 said account introduced a change to Google’s OSS Fuzzer to weaken detection for XZ.
Somebody played a years long game of Jenga and lost.
Before everybody high fives each other, this is how the backdoor was found: somebody happened to look at why CPU usage had increased in sshd, and did all the research and notification work themselves. By this point the backdoor had been there for a month unnoticed.
I’ve made the joke before that if GCHQ aren’t introducing backdoors and vulns in open source that I want a tax refund. It wasn’t a joke. And it won’t be just be GCHQ.
Another two thoughts on XZ -
- sshd itself has no dependency on the XZ utils library. The streams got crossed in a way I don’t think anybody understood (except the threat actor).
- had that backdoor been performant with sshd, I don’t think anybody would have spotted it.
The way this played out opens a window of opportunity to go back and look at both issues.
Really good timeline of what is known to have happened so far. It looks like the rogue developer deliberately introduced a vulnerability in other package, too - I haven’t seen anybody else mention this.
Reading the dev’s GitHub history, they’ve been making changes to other open source projects too around compression. It also appears they/somebody involved has other accounts, too.
https://boehs.org/node/everything-i-know-about-the-xz-backdoor
How far the rabbit hole goes - back in 2021 they deliberately introduced a risky change in the compression library libarchive. Nobody noticed. This is shipped in a ton of systems:
https://github.com/libarchive/libarchive/pull/1609
Whoever the threat actor is knows what they are doing as they’ve gone after chained dependencies around compression.
Added the error text when printing out warning and errors in bsdtar when untaring. Previously, there were cryptic error messages when, for example in issue #1561, the user tries to untar an archive...
If anybody thinks this kind of thing is unique, it isn’t.
Example - CVE-2021-44529 in Ivanti Endpoint Manager. The cause?
Backdoor in open source code, was there for 7 years.
XZ Embedded Linux kernel module for IoT devices, 10 days ago had a change submitted to add Jia Tan (backdoor author) as a maintainer.
https://lore.kernel.org/lkml/202403201[email protected]/
Linux kernel documentation: https://docs.kernel.org/staging/xz.html
The GitHub repository for XZ Embedded kernel module has also been disabled: https://github.com/tukaani-project/xz-embedded/
Original maintainer of XZ repos has posted a short update:
https://tukaani.org/xz-backdoor/
HT @SamantazFox
The poor original maintainer of xz is on it now, and has already found another "fun" thing: https://git.tukaani.org/?p=xz.git;a=commitdiff;h=f9cf4c05edd14dedfe63833f8ccbe41b55823b00 . The configure check for enabling the Landlock sandboxing facility was subtly broken, so that Landlock support would never get enabled. The original malicious commit landed around the same timeframe as the main backdoor, also at an abnormal time of day compared to the new maintainer's historical activity pattern.
Also since there’s a lot going on here, up thread I mentioned a 2015 minor bug in Google’s OSS Fuzzer (security testing tool) - the threat actor deliberately introduced the bugged function into XZ, then used that to get an exception in OSS Fuzzer’s code to stop scanning of XZ.
I’ve just been looking at the actual backdoor for a few hours with greater minds than me, it’s incredibly complex - it basically piggy backs RSA key RCE inside sshd as a Trojan horse. Somebody/bodies spent $$ on this.
Also, to be super clear nobody should panic about #XZ as the Postgres developer who found this basically caught it quick enough that almost no businesses or devices will be running the code.
So everybody should be chill about this specific issue as that guy saved everybody’s bacon.
To give an idea of the scale of OpenSSH usage, it’s absolutely huge, it dwarfs RDP by a huge margin (think ten times), and had this survived for a long period of time it would have been unbelievably bad.
The sshd backdoor in #XZ is just way beyond my technical ability. There’s so much there, I imagine more than a few conference talks are going to be submitted for it.
My amateur hour view is it’s really well put together (eg you can only execute commands if you have a private key that only the attacker has) and appears to allow remote removal of the backdoor, too. There’s a whole bunch of features which I’m too dumb to get.
Also for me, performance isn’t that bad - I wouldn’t have noticed it.
Kinda interesting - a change made by the threat actor has ended up in Windows OS. Redmond bundled libarchive into the OS, which the TA had been tinkering with.
This is the code change which has been imported: https://github.com/libarchive/libarchive/pull/1609
Edit: reworded this as the scope looks bigger than Win 11.
Added the error text when printing out warning and errors in bsdtar when untaring. Previously, there were cryptic error messages when, for example in issue #1561, the user tries to untar an archive...
4 days since XZ backdoor became public knowledge and most major Linux AV and EDR security vendors still have zero detections.. they haven’t even set the static file hashes as malicious.
Can’t wait for all the vendor blogs in a week saying they fully protect against the threat. 👍
.@amlw wrote a great proof of concept for #XZ to allow code execution via ssh.
Very important note: it doesn’t work in the wild as you need the private key, which only the threat actor(s) have. But you can create your own for exploiting your own servers.
If you use Microsoft Vulnerability Management, it is false positiving on CVE-2024-3094 aka #XZ backdoor - it is picking up the Cygwin version of XZ as vuln on Windows systems.
The Cygwin packages predate the backdoor and it doesn’t impact Windows, also the file it flags isn’t the backdoor but lzmadec.exe
Re #XZ attacker - the known threat actor account made various changes across multiple open source projects and documentation.
Library maintainers should not look at those changes in isolation of just that line change, or assume the threat actor only became malicious later. Assume they are very well resourced and acting with broad objectives.
In at least one case they made an existing unknown vulnerability exploitable, and we know they were socially engineering the XZ maintainer years ago.
‘They’ are very likely a multi million dollar operation - see also just the shell script analysis, before you even get to the backdoor (which is much more nuts) https://research.swtch.com/xz-script
The actual SSH backdoor is cryptographically signed so only the threat actor can use it. If you work in threat intelligence and write “foreign” intelligence agency, you might want to look at your bias training.
@GossiTheDog Curious that they marked Alpine Linux as not affected: Unit 42 links 5.6 versions prior to 5.6.1-r2 as impacted and the link also shows as much:
@GossiTheDog Crap, I didn't realize that OpenSUSE MicroOS was rolling release.
And indeed, I had the backdoor installed on my server for a month.
Guess it's time to wipe the server and reinstall from scratch... It gives a good reason to check the backups and Ansible configs :v
On the very first day I’ve submitted the static “test” files to ClamAV and VT. ClamAV response was:
Our initial assessment shows that this file is possibly clean. If you provided a description that suggests otherwise, we will further examine the sample & proceed from there.
On VT the detection rate was zero but you can at least add a comment and community ranking there, which I did. Now I see it’s detected by 7/60 and more community ratings were added.
@GossiTheDog This is a pretty big wakeup call, to be honest.
I also wonder if they've managed to sneak in other code that has NOT been caught yet.
@GossiTheDog I think this was for the BSD tar executable, so you have to run the code deliberately:
C:\>tar.exe --version
bsdtar 3.6.2 - libarchive 3.6.2 zlib/1.2.5.f-ipp liblzma/5.2.5 bz2lib/1.0.8 libzstd/1.5.4
@GossiTheDog And we only know that because they re-used accounts/names for both code submissions, right?
That's a disturbing thought.
@sheogorath @GossiTheDog ok. debian seems to be "confident enough" now 😁
@[email protected] @[email protected] Confident enough.
I don't know which is the biggest crime: naming a product or service with a word of the English language, like "upstream", or mentioning that product or service in an article without capitalizing, changing the font, or qualifiying it -- as "software from upstream" rather than "software from Upstream" or "software from the /upstream/ site".
@0daystolive @GossiTheDog @SamantazFox
Blush. OK. Then the criminal charges are hereby reduced to a mere misdemeanor: use of confusing jargon. A few weeks of community service will do.
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