How the xz backdoor highlights a major flaw in Nix
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The main issue is the handling of security updates within the Nixpkgs ecosystem, which relies on Nix's CI system, Hydra, to test and build packages. Due to the extensive number of packages in the Nixpkgs repository, the process can be slow, causing delays in the release of updates. As an example, the updated xz 5.4.6 package took nearly 5 days to become available in the unstable branch!
Fundamentally, there needs to be a change in how security fixes are handled in Hydra. As stated in the article, Nix was lucky to be unaffected, but multiple days to push out a security patch of this severity is concerning, even if there was no reason for concern.
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Were systems in the stable branch at risk of compromise? Were there delays in releasing security fixes in the stable branch.
I don't even think unstable was suseptical to it. I don't think Nix ties ssh to systemd. Debian and redhat do.
It was not vulnerable to this particular attack because the attack didn't specifically target Nixpkgs. It could have very well done so if they had wanted to.
Anyway the xz backdoor was enabled only in rpm and deb packages.
AFAIK it was enabled in anything that used the official source tarball. The exploit binaries were added during the tarball build process.
Nope. There were checks of build environment.
Then why did all distros issue a fix for the package?
Because nobody can be sure there are no other backdoors. And, I guess, they wanted to stop distribution of affected source code.
Shouldn't the lesson here be "don't introduce more complexity and dependencies to critical software"?
But then again that's systemd in a nutshell...
AFAIK, affected versions never made it to stable as there was no reason to backport it.