The person that found this is a hero.
Whenever I see slightly weird behaviour, there is a temptation to just move on because there isn’t enough time, running software is complicated, and there is something else I want to do. I will try to change my attitude in future in case it uncovers a backdoor like this – it would be educational too.
A nice tl;dr was https://news.ycombinator.com/item?id=39866307
Copied here:
For those panicking, here are some key things to look for, based on the writeup:
-
A very recent version of liblzma5 - 5.6.0 or 5.6.1. This was added in the last month or so. If you’re not on a rolling release distro, your version is probably older.
-
A debian or RPM based distro of Linux on x86_64. In an apparent attempt to make reverse engineering harder, it does not seem to apply when built outside of deb or rpm packaging. It is also specific to Linux.
-
Running OpenSSH sshd from systemd. OpenSSH as patched by some distros only pulls in libsystemd for logging functionality, which pulls in the compromised liblzma5.
Debian testing already has a version called ‘5.6.1+really5.4.5-1’ that is really an older version 5.4, repackaged with a newer version to convince apt that it is in fact an upgrade.
It is possible there are other flaws or backdoors in liblzma5, though.
5.6.1+really5.4.1
Most sane Debian package management
-
Additional relevant discussion on HN: https://news.ycombinator.com/item?id=39865810
Very annoying - the apparent author of the backdoor was in communication with me over several weeks trying to get xz 5.6.x added to Fedora 40 & 41 because of it’s “great new features”. We even worked with him to fix the valgrind issue (which it turns out now was caused by the backdoor he had added). We had to race last night to fix the problem after an inadvertent break of the embargo.
He has been part of the xz project for 2 years, adding all sorts of binary test files, and to be honest with this level of sophistication I would be suspicious of even older versions of xz until proven otherwise.
Damn. I would love to see a full post mortem on this compromise.
The hack is still not fully understood and is being analyzed. It doesn’t help that Github suspended everything, including the original maintainer’s account (who is believed to be a victim of social engineering).
Anyway, you will eventually see a post mortem. I’m willing to bet that it’s going to be as phenomenal as the hack itself. The case and its investigation is going to be a classic case study for all security researchers and security-minded users. Anyway, I doubt that the attackers will ever be found. Jia Tan, Jigar Kumar and others are going to remain as ghosts like Satoshi Nakamoto.
