Background On Friday, March 29th, 2024, a historical and sophisticated security vulnerability (CVE-2024-3094) was discovered in the XZ Utils package and liblzma api in version 5.6.0 and 5.6.1. While this vulnerability mostly affects Debian and RedHat distributions, there was some interesting discussion regarding xz and Nix.
How did this affect Nix and NixOS? The truth is not a whole lot in reality. I saw conflicting reports, but supposedly, the tarballs of xz that Nix downloads were not infected.
You are right, it will be a mess to pull xz from a different hash. This is why you go back to an older build, and keep only packages you need on the newer version.
Those packages themselves depend on xz. Pretty much all of them.
What you’re suggesting would only make the
xzexecutable not be backdoored anymore but any other application using liblzma would still be as vulnerable as before. That’s actually the only currently known attack vector; inject malicious code into SSHD via liblzma.