Vulnerability in Nix 2.24

Announcements Security
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There’s a vulnerability in Nix 2.24.

If you’re using the regular nix from nixpkgs (which the vast majority of users will be), you’re still on a safe version. If you recently (after August 1st) installed nix using the nix (not NixOS) installers, or are using nixVersions.git from nixpkgs, then you need to double-check. A fix is expected in version 2.24.6 which is to be released soon.

GHSA-h4vv-h3jq-v493

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To summarize:

  • This vulnerability allows privilege escalation, so it’s serious
  • It only affects Nix 2.24.0 to 2.24.5
  • The known attack vectors are closed in Nix 2.24.6

Please excuse any delay; we will publish a post mortem once the acute situation is cleaned up.

In the meantime, if you installed or upgraded Nix recently (after 2024-08-01 and before 2024-09-10):

Lix is not affected because it was forked off Nix 2.18. The vulnerability was reported by Lix core team member @puckipedia.

Mentioned elsewhere, for reference:

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The GitHub advisory is now public: Unsafe NAR unpacking · Advisory · NixOS/nix · GitHub

And 2.24.6 is released: Release 2.24.6 · NixOS/nix · GitHub

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Thanks for the quick fixes now that the exploit is public.

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I saw the remedy was about case insensitivity. I suppose case sensitive filesystems are not affected?

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How so? The original explanation mentioned it was due to improper hash verification and symlink handling

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Case-sensitivity was only one of the vectors. There are a class of similar bugs that abuse a similar mechanism of defining a symlink with an arbitrary target and then later traversing that symlink as a way to get write access as root. Other mechanisms include messing with the ordering of NAR entries and unicode representations.

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Here’s the post mortem as promised:

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