How the xz backdoor highlights a major flaw in Nix | Shade's Blog
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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.

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.

  • bizdelnick
    51·
    9 months ago

    Anyway the xz backdoor was enabled only in rpm and deb packages.

    • lemmyvore@feddit.nlEnglish
      21·
      9 months ago

      AFAIK it was enabled in anything that used the official source tarball. The exploit binaries were added during the tarball build process.

      • bizdelnick
        41·
        9 months ago

        Nope. There were checks of build environment.

          • bizdelnick
            6·
            9 months ago

            Because nobody can be sure there are no other backdoors. And, I guess, they wanted to stop distribution of affected source code.