The malicious changes were submitted by JiaT75, one of the two main xz Utils developers with years of contributions to the project.
“Given the activity over several weeks, the committer is either directly involved or there was some quite severe compromise of their system,” an official with distributor OpenWall wrote in an advisory. “Unfortunately the latter looks like the less likely explanation, given they communicated on various lists about the ‘fixes’” provided in recent updates. Those updates and fixes can be found here, here, here, and here.
On Thursday, someone using the developer’s name took to a developer site for Ubuntu to ask that the backdoored version 5.6.1 be incorporated into production versions because it fixed bugs that caused a tool known as Valgrind to malfunction.
“This could break build scripts and test pipelines that expect specific output from Valgrind in order to pass,” the person warned, from an account that was created the same day.
One of maintainers for Fedora said Friday that the same developer approached them in recent weeks to ask that Fedora 40, a beta release, incorporate one of the backdoored utility versions.
“We even worked with him to fix the valgrind issue (which it turns out now was caused by the backdoor he had added),” the Ubuntu maintainer said.
He has been part of the xz project for two years, adding all sorts of binary test files, and with this level of sophistication, we would be suspicious of even older versions of xz until proven otherwise.
Having once worked on an open source project that dealt with providing anonymity - it was considered the duty of the release engineer to have an overview of all code committed (and to ask questions, publicly if needed, if they had any doubts) - before compiling and signing the code.
On some months, that was a big load of work and it seemed possible that one person might miss something. So others were encouraged to read and report about irregularities too. I don’t think anyone ever skipped it, because the implications were clear: “if one of us fails, someone somewhere can get imprisoned or killed, not to speak of milder results”.
However, in case of an utility not directly involved with functions that are critical for security - it might be easier to pass through the sieve.
I’ve actually seen people checking in code that doesn’t get reviewed properly on mission critical apps before (like in the health industry).
My understanding is basically the same as yours, and in theory I agree with you. However, the problem is we all tend to hand-wave away any possibility of bad things happening, because it’s open source, and don’t take into account human nature, especially when it comes to volunteer versus paid work.