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Story of XZ Backdoor [video]

132 points by Ulf950

by II2II

2 subcomments

Even though the video is somewhat sensationalized at some points, it is well worth a watch for people who are interested in computers but don't have a background in it. There is a nice mixture of everything from history (e.g. the founding of the FSF) to a clear explanation of a compression algorithm (clear enough that one should be able to implement it). It also makes claims that should make some people stop and think about the industry as a whole (such as Linux being the most important contemporary operating system).
I'm not sure if it is HN-crowd type material since it is easy enough information for most of us to dig up, assuming we didn't already know it. Yet it does not simplify things to the point of, "technology is magic."

by coldpie

3 subcomments

This is IMO one of the coolest tech stories to ever happen, seriously amazing spycraft & hacking skills, but I haven't been keeping up with new developments from this story since it broke. Last I heard, the best guess at what happened was some state-sponsored actor worked very hard to get this merged, and it was caught luckily at the last minute. But no one had any smoking gun as to who did it or why or who they were targeting. Any new developments since then? Are we still just totally in the dark about what was going on here?

by ting0

1 subcomments

https://boehs.org/node/everything-i-know-about-the-xz-backdo...
This is the scariest part to me:
> A pull request (https://github.com/jamespfennell/xz/pull/2) to a go library by a 1Password employee is opened asking to upgrade the library to the vulnerable version

by k2enemy

0 subcomment

Oxide and Friends also had a great podcast with Andres about the discovery:
https://oxide-and-friends.transistor.fm/episodes/discovering...

by forinti

3 subcomments

Ireland recently created a Basic Income scheme for artists.
Europe should have an equivalent scheme for programmers of important Open Source projects such as this one.

by sricharanbattu

0 subcomment

I had a question. People are claiming that the spike in time for ssh or the performance degradation is not much.
But in the video itself, they show that the actual ssh time was about 100 ms and the new time it took was about 600 ms. It is almost 6 times the actual time. I am expecting the performance of the benchmark to significantly drop with these times. And it should be obvious to see that something was wrong.
( I am taking nothing from Andres here. I think he's a brilliant engineer to actually find the root cause of this himself. He is a hero. I am just pointing that 500 ms is not something obscure time interval).

by amiga386

4 subcomments

Lovely video, going into almost everything...
...and yet, zero mention of systemd's recommendation for programs to link in the libsystemd kitchen sink just to call sd_notify() (which should really be its own library)
...and no mention of why systemd felt the need to preemptively load compression libraries, which it only needs to read/write compressed log files, even if you don't read/write log files at all? Again, it's a whole independent subsystem that could be its own library.
The video showed that xz was a dependency of OpenSSH. It showed on screen, but never said aloud, that this was only because of systemd. Debian/Redhat's sshd [0] was started with systemd and they added in a call to the sd_notify() helper function (which simply sends a message to the $NOTIFY_SOCKET socket), just to inform systemd of the exact moment sshd is ready. This loads the whole of libsystemd. That loads the whole of liblzma. Since the xz backdoor, OpenSSH no longer uses the sd_notify() function directly, it writes its own code to connect to $NOTIFY_SOCKET. And the sd_notify manpage begrudgingly gives a listing of code you can use to avoid calling it, so if you're an independent program with no connection to systemd, you just want to notify it you've started... you don't need to pull in the libsystemd kitchen sink. As it should've been in the first place.
Is the real master hacker Lennart Poettering, for making sure his architectural choices didn't appear in this video?
[0]: as an aside, the systemd notification code is only in Debian, Redhat et al because OpenSSH is OpenBSD's fork of Tatu Ylönen's SSH, which went on to become proprietary software. systemd is Linux-only and will never support OpenBSD, so likewise OpenBSD don't include any lines of code in OpenSSH to support systemd. Come to think of it, "BSD" is another thing they don't mention in the script, despite mentioning the AT&T lawsuit (https://en.wikipedia.org/wiki/USL_v._BSDi)

by dijit

2 subcomments

I actually watched this last night, and while I totally understand that criticism is easy, and making things is hard (and the production quality here is great); I got a weird vibe from the video when it comes to who it is for.
The technical explanations are way too complex (even though they're "dumbed down" somewhat with the colour mixing scenario), that anyone who understands those will also know about how dependencies work and how Linux came to be.
It feels almost like it's made for people like my mum, but it will lose them almost immediately at the first mention of complex polynomials.
The actual weight of the situation kinda lands though, and that's important. It's really difficult to overstate how incredibly lucky we were to catch it, and how sophisticated the attack actually was.
I'm really sad that we will genuinely never know who was behind it, and anxious that such things are already in our systems.

0 subcomment

by mbauman

2 subcomments

I'm still floored that Andres both found this and didn't ignore it. It's such a testament to an incredible engineer.
(But also, my conspiratorially-inclined mind is quite entertained by the thought of some sort of parallel construction or tip from a TLA.)

by TacticalCoder

0 subcomment

Something that's puzzling in that XZ backdoor attempt is that the attacker had to hide the evil payload. And he hid it in test files and AIUI it was injected at build time through a modified build script and that went unnoticed (it's a compiled, deployed, version that got caught by someone and raised alarm bell).
Why are build scripts not operating in a clean directory, stripping away all test related files?
Isn't this something we should begin to consider doing, seen that it's all too easy to put arbitrary things in test files (you can just pretend stuff is "fuzzed" or "random" or "test vectors" and whatnots: there's always going to be room to hide mischief in test files)?
Like literally building, but only after having erased all test directories/files/data.
Or put it this way: how many backdoors are actually live but wouldn't be if every single build was only done after carefully deleting all the irrelevant files related to tests?