- cross-posted to:
- [email protected]
- cross-posted to:
- [email protected]
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Thank you open source for the transparency.
And thank you Microsoft.
Shocking, but true.
They just pay some dude that is doing good work
The tukaani github repos are gone, is there a mirror somewhere?
Tukaani main website
Though unfortunately (or I guess for most use-cases fortunately) you can’t find the malicious m4/build-to-host.m4 file on there afaik. The best way to find that now, should you really want to, is by looking through the commit history of the salsa.debian.org/debian/xz-utils repository which is, as far as I understand it, the repository that the debian packages are built from and consequently also what the compromised packages were built from.
this was one hell of an april fools joke i tell you what.
Imagine
i mean, to some degree, it is.
A small blurb from The Guardian on why Andres Freund went looking in the first place.
So how was it spotted? A single Microsoft developer was annoyed that a system was running slowly. That’s it. The developer, Andres Freund, was trying to uncover why a system running a beta version of Debian, a Linux distribution, was lagging when making encrypted connections. That lag was all of half a second, for logins. That’s it: before, it took Freund 0.3s to login, and after, it took 0.8s. That annoyance was enough to cause him to break out the metaphorical spanner and pull his system apart to find the cause of the problem.
The post on the oss is more detailed and informative
This is informative, but unfortunately it doesn’t explain how the actual payload works - how does it compromise SSH exactly?
It allows a patched SSH client to bypass SSH authentication and gain access to a compromised computer
From what I’ve heard so far, it’s NOT an authentication bypass, but a gated remote code execution.
There’s some discussion on that here: https://bsky.app/profile/filippo.abyssdomain.expert/post/3kowjkx2njy2b
But it would be nice to have a similar digram like OP’s to understand how exactly it does the RCE and implements the SSH backdoor. If we understand how, maybe we can take measures to prevent similar exploits in the future.
I think ideas about prevention should be more concerned with the social engineering aspect of this attack. The code itself is certainly cleverly hidden, but any bad actor who gains the kind of access as Jia did could likely pull off something similar without duplicating their specific method or technique.
Ideally you need a double-blind checking mechanism definitionally impervious to social engineering.
That may be possible in larger projects but I doubt you can do much in where you have very few maintainers.
I bet the lesson here for future attackers is: do not affect start-up time.
I imagine if this attacker wasn’t in a rush to get the backdoor into the upcoming Debian and Fedora stable releases he would have been able to notice and correct the increased CPU usage tell and remain undetected.
Under the right circumstances this interference could potentially enable a malicious actor to break sshd authentication and gain unauthorized access to the entire system remotely. —Wikipedia, sourced to RedHat
Of course, the authentication bypass allows remote code execution.
I am not a security expert, but the scenario they describe sounds exactly like authentication bypass to a layman like me.
According to https://www.youtube.com/watch?v=jqjtNDtbDNI the software installs a malicious library that overwrite the signature verification function of ssh.
I was wondering if the bypass function was designed to be slightly less resource intensive, it probably won’t be discovered and will be shipped to production.
Also I have mixed feeling about dynamic linking, on the one hand, it allows projects like harden malloc to easily integrate into the system, on the other hand, it also enables the attacker to hijack the library in a similar fashion.
EDIT: This is a remote code execution exploit, not authentication bypass. The payload is sent as an authentication message and will be executed by the compromised authentication function.
This means:
- the payload will be executed as root, since sshd run as root.
- the payload will leave no trace in login log.
So this is much worse than ssh authentication bypass.
Here is an alternative Piped link(s):
https://www.piped.video/watch?v=jqjtNDtbDNI
Piped is a privacy-respecting open-source alternative frontend to YouTube.
I’m open-source; check me out at GitHub.
5.6.1 in fact made it less resources-intensive, but the distro happened to not have updated yet when Freund discovered the backdoor.
Authentication bypass should give you interactive access. “I’m in” like. Remote code execution only allows you to run a command, without permanent access. You can use some RCE vulnerabilities to bypass authentication, but not all.
Yeah, but the malicious code replaces the ssh signature verification function to let it allow a specific signature. Hence attacker, with the key, can ssh into any system without proper authentication by ssh.This kind of describes authentication by-pass, not just remote code execution…EDIT: it is remote code execution, see the edit of parent comment.
Somebody wrote a PoC for it: https://github.com/amlweems/xzbot#backdoor-demo
Basically, if you have a patched SSH client with the right ED448 key you can have the gigged sshd on the other side run whatever commands you want. The demo just does
id > /tmp/.xzbut it could be whatever command you want.
There is RedHat’s patch for OpenSSH that adds something for systemd, which adds libsystemd as dependency, which has liblzma as its own dependency.
I do believe it does
Any additional information been found on the user?
Probably Chinese?
They’re more likely to be based in Eastern Europe based on the times of their commits (during working hours in Eastern European Time) and the fact that while most commits used a UTC+8 time zone, some of them used UTC+2 and UTC+3: https://rheaeve.substack.com/p/xz-backdoor-times-damned-times-and
It is also hard to be certain as they could be a night owl or a early riser.
Yeah - The post goes into a lot of detail, and they did take that into account. It’s worth reading.
Can’t confirm but unlikely.
Via https://boehs.org/node/everything-i-know-about-the-xz-backdoor
They found this particularly interesting as Cheong is new information. I’ve now learned from another source that Cheong isn’t Mandarin, it’s Cantonese. This source theorizes that Cheong is a variant of the 張 surname, as “eong” matches Jyutping (a Cantonese romanisation standard) and “Cheung” is pretty common in Hong Kong as an official surname romanisation. A third source has alerted me that “Jia” is Mandarin (as Cantonese rarely uses J and especially not Ji). The Tan last name is possible in Mandarin, but is most common for the Hokkien Chinese dialect pronunciation of the character 陳 (Cantonese: Chan, Mandarin: Chen). It’s most likely our actor simply mashed plausible sounding Chinese names together.
That actually suggests not Chinese due to naming inconsistencies
Could be Chinese creating reasonable doubt. Making this sort of mistake makes explanations that this wasn’t Chinese sound plausible. Even if evidence other than the name comes out, this rebuttal can be repeated and create confusion amongst the public, reasonable suspicions against accusers and a plausible excuse for other states to not blame China (even if they believe it was China).
Confusion and multiple narratives is a technique carried out often by Soviet, Russian and Chinese government. We are unlikely to be able to answer the question ourselves. It will be up to the intelligence agencies to do that.
If someone wanted to blame China for this, they would take the name of a real Chinese person to do it. There is over a billion real people they could take a name from. It unlikely that a person creating a name for someone for this type of espionage would make a mistake like picking an implausible name accidentally.
They’re more likely to be based in Eastern Europe based on the times of their commits (during working hours in Eastern European Time) and the fact that while most commits used a UTC+8 time zone, some of them used UTC+2 and UTC+3: https://rheaeve.substack.com/p/xz-backdoor-times-damned-times-and
I’m not suggesting one way or another, only that the quoted explanation taken at face value isn’t suggesting China based on name analysis.
There’s also no reason to assume a nation state. This is completely within the realm of a single or small group of hackers. Organized crime another possibility. Errors with naming are plausible just as the initial mistakes with timing analysis and valgrind errors.
Even assuming a nation state, you name Russia as a possibility. Russia has shown themselves to be completely capable of errors, in their hacks (2016 election interference that was traced back to their intelligence base), their wars, their assassination attempts, etc.
And to me it doesn’t seem any more likely that China would point to themselves but sprinkle doubt with inconsistent naming versus just outright pointing to someone else.
It’s all guesses, nothing points one way or another. I think we agree on that.
A big part of it is also letting other people know you did it. China and Russia are big on this. The create dangerous situations, then say they aren’t responsible all while sowing confusion. The want plausible deniability, confusion and credit for doing it.
So this doesn’t really tell us one way or the other who this person is or isn’t.
Just because somebody picked a vaguely Chinese-sounding handle doesn’t mean much about who or where.
That’s why I put the question mark
as long as you’re up to date on everything here: https://boehs.org/node/everything-i-know-about-the-xz-backdoor
the only additional thing i’ve seen noted is a possibilty that they were using Arch based on investigation of the tarball that they provided to distro maintainers
If this was done by multiple people, I’m sure the person that designed this delivery mechanism is really annoyed with the person that made the sloppy payload, since that made it all get detected right away.
I hope they are all extremely annoyed and frustrated
Inconvenienced, even.
Inconceivable!
I like to imagine this was thought up by some ambitious product manager who enthusiastically pitched this idea during their first week on the job.
Then they carefully and meticulously implemented their plan over 3 years, always promising the executives it would be a huge pay off. Then the product manager saw the writing on the wall that this project was gonna fail. Then they bailed while they could and got a better position at a different company.
The new product manager overseeing this project didn’t care about it at all. New PM said fuck it and shipped the exploit before it was ready so the team could focus their work on a new project that would make new PM look good.
The new project will be ready in just 6-12 months, and it is totally going to disrupt the industry!
I see a dark room of shady, hoody-wearing, code-projected-on-their-faces, typing-on-two-keyboards-at-once 90’s movie style hackers. The tables are littered with empty energy drink cans and empty pill bottles.
A man walks in. Smoking a thin cigarette, covered in tattoos and dressed in the flashiest interpretation of “Yakuza Gangster” imaginable, he grunts with disgust and mutters something in Japanese as he throws the cigarette to the floor, grinding it into the carpet with his thousand dollar shoes.
Flipping on the lights with an angry flourish, he yells at the room to gather for standup.
Cigarette is stomped.
Stickies fall from kanban board.
Backdoor dishonor.
I think going forward we need to look at packages with a single or few maintainers as target candidates. Especially if they are as widespread as this one was.
In addition I think security needs to be a higher priority too, no more patching fuzzers to allow that one program to compile. Fix the program.
I’d also love to see systems hardened by default.
This has always been the case. Maybe I work in a unique field but we spend a lot of time duplicating functionality from open source and not linking to it directly for specifically this reason, at least in some cases. It’s a good compromise between rolling your own software and doing a formal security audit. Plus you develop institutional knowledge for that area.
And yes, we always contribute code back where we can.
We run our forks not because of security, but because pretty much nothing seems to work for production use without some source code level mods.
In the words of the devs in that security email, and I’m paraphrasing -
“Lots of people giving next steps, not a lot people lending a hand.”
I say this as a person not lending a hand. This stuff over my head and outside my industry knowledge and experience, even after I spent the whole weekend piecing everything together.
You are right, as you note this requires a set of skills that many don’t possess.
I have been looking for ways I can help going forward too where time permits. I was just thinking having a list of possible targets would be helpful as we could crowdsource the effort on gitlab or something.
I know the folks in the lists are up to their necks going through this and they will communicate to us in good time when the investigations have concluded.
Packages or dependencies with only one maintainer that are this popular have always been an issue, and not just a security one.
What happens when that person can’t afford to or doesn’t want to run the project anymore? What if they become malicious? What if they sell out? Etc.
What if the repository becomes stupid and takes a package away from a developer and said developer deletes his other packages. See leftpad.
There’s gotta be a better way to verify programs then just what the devs do. For example patching the fuzzer, that should be seen as a clear separation of duties problem.
That constant issue of low Dev/high use dependencies is awful and no one I’ve met on the business end can seem to figure out that need to support those kind of people or accept, what should frankly be, legal liability for what goes wrong. This isn’t news its just a cover song. And its not an open source problem, its just a software problem. (
no more patching fuzzers to allow that one program to compile. Fix the program
Agreed.
Remember Debian’s OpenSSL fiasco? The one that affected all the other derivatives as well, including Ubuntu.
It all started because OpenSSL did add to the entropy pool a bunch uninitialized memory and the PID. Who the hell relies on uninitialized memory ever? The Debian maintainer wanted to fix Valgrind errors, and submitted a patch. It wasn’t properly reviewed, nor accepted in OpenSSL. The maintainer added it to the Debian package patch, and then everything after that is history.
Everyone blamed Debian “because it only happened there”, and definitely mistakes were done on that side, but I surely blame much more the OpenSSL developers.
OpenSSL did add to the entropy pool a bunch uninitialized memory and the PID.
Did they have a comment above the code explaining why it was doing it that way? If not, I’d blame OpenSSL for it.
The OpenSSL codebase has a bunch of issues, which is why somewhat-API-compatible forks like LibreSSL and BoringSSL exist.
I’d have to dig it, but I think it said that it added the PID and the uninitialized memory to add a bit more data to the entropy pool in a cheap way. I honestly don’t get how that additional data can be helpful. To me it’s the very opposite. The PID and the undefined memory are not as good quality as good randomness. So, even without Debian’s intervention, it was a bad idea. The undefined memory triggered valgrind, and after Debian’s patch, if it weren’t because of the PID, all keys would have been reduced to 0 randomness, which would have probably raised the alarm much sooner.
.
It was Spez trying to collect more user data to make Reddit profitable
Probably a state actor
The CIA will know, we will most likely not.
We probably never will.
If we ever do, it’ll be 40 or 50 years from now.
In a nutshell you say…
Coconut at least…
I’m going to read it later, but if I don’t find a little red Saddam Hussein hidden in there I’ll be disappointed
edit: eh my day wasn’t good anyway
Don’t forget all of this was discovered because ssh was running 0.5 seconds slower
Technically that wasn’t the initial entrypoint, paraphrasing from https://mastodon.social/@AndresFreundTec/112180406142695845 :
It started with ssh using unreasonably much cpu which interfered with benchmarks. Then profiling showed that cpu time being spent in lzma, without being attributable to anything. And he remembered earlier valgrind issues. These valgrind issues only came up because he set some build flag he doesn’t even remember anymore why it is set. On top he ran all of this on debian unstable to catch (unrelated) issues early. Any of these factors missing, he wouldn’t have caught it. All of this is so nuts.
Its toooo much bloat. There must be malware XD linux users at there peak!
Tbf 500ms latency on - IIRC - a loopback network connection in a test environment is a lot. It’s not hugely surprising that a curious engineer dug into that.
Especially that it only took 300ms before and 800ms after
Is that from the Microsoft engineer or did he start from this observation?
From what I read it was this observation that led him to investigate the cause. But this is the first time I read that he’s employed by Microsoft.
I’ve seen that claim a couple of places and would like a source. It very well may be since Microsoft prefers Debian based systems for WSL and for azure, but its not something I would have assumed by default
His LinkedIn, his Twitter, his Mastodon, and the Verge, for starters.
It’s in his mastodon bio. https://mastodon.social/@AndresFreundTec/112180083704606941
Thank you!
AFAIK he works on the Azure PostgreSQL product.
but it’s* not something
Postgres sort of saved the day
RIP Simon Riggs
Half a second is a really, really long time.
reminds of Data after the Borg Queen incident
Which ep/movie are you referring to?
The one where they go back in time but the whales were already nuked
I… actually can’t tell if you’re taking the piss or if that’s a real episode.
I have so many questions about the whales.
Star Trek: First Contact
If this exploit was more performant, I wonder how much longer it would have taken to get noticed.
I have been reading about this since the news broke and still can’t fully wrap my head around how it works. What an impressive level of sophistication.
And due to open source, it was still caught within a month. Nothing could ever convince me more than that how secure FOSS can be.
Yea, but then heartbleed was a thing for how long that no-one noticed?
The value of foss is so many people with a wide skill set can look at the same problematic code and dissect it.
Can be, but isn’t necessarily.
Idk if that’s the right takeaway, more like ‘oh shit there’s probably many of these long con contributors out there, and we just happened to catch this one because it was a little sloppy due to the 0.5s thing’
This shit got merged. Binary blobs and hex digit replacements. Into low level code that many things use. Just imagine how often there’s no oversight at all
I was literally compiling this library a few nights ago and didn’t catch shit. We caught this one but I’m sure there’s a bunch of “bugs” we’ve squashes over the years long after they were introduced that were working just as intended like this one.
The real scary thing to me is the notion this was state sponsored and how many things like this might be hanging out in proprietary software for years on end.
Yes, and the moment this broke other project maintainers are working on finding exploits now. They read the same news we do and have those same concerns.
I wonder if anyone is doing large scale searches for source releases that differ in meaningful ways from their corresponding public repos.
It’s probably tough due to autotools and that sort of thing.
Very generous to imagine that maintainers have so much time on their hands
Bug fixes can be delayed for a security sweep. One of the quicker ways that come to mind is checking the hash between built from source and the tarball
The whole point here is that the build process was infiltrated - so you’d have to remake the build system yourself to compare, and that’s not a task that can be automated
The scary thing about this is thinking about potential undetected backdoors similar to this existing in the wild. Hopefully the lessons learned from the xz backdoor will help us to prevent similar backdoors in the future.
I think we need focus on zero trust when it comes to upstream software
exactly, stop depending on esoteric libraries
It is fine to use them just know how they work and check the commit log.
That of course requires you to pull from got instead of a tarball
this was well hidden. not sure anyone would have spotted this by checking commit log
It was hidden in the Tarball
i’m not an expert, but my reading was that it was hidden in a binary used for testing EDIT: oh yeah, i see what you mean
