An issue was discovered in the nix crate 0.16.0 and later before 0.20.2, 0.21.x before 0.21.2, and 0.22.x before 0.22.2 for Rust. unistd::getgrouplist has an out-of-bounds write if a user is in more than 16 /etc/groups groups.

Nix is a package manager for Linux and other Unix systems. A fixed-output derivations on Linux can send file descriptors to files in the Nix store to another program running on the host (or another fixed-output derivation) via Unix domain sockets in the abstract namespace. This allows to modify the output of the derivation, after Nix has registered the path as "valid" and immutable in the Nix database. In particular, this allows the output of fixed-output derivations to be modified from their expected content. This issue has been addressed in versions 2.3.18 2.18.2 2.19.4 and 2.20.5. Users are advised to upgrade. There are no known workarounds for this vulnerability.

Nix is a package manager for Linux and other Unix systems. On macOS, built-in builders (such as builtin:fetchurl, exposed to users with import <nix/fetchurl.nix>) were not executed in the macOS sandbox. Thus, these builders (which are running under the nixbld users) had read access to world-readable paths and write access to world-writable paths outside of the sandbox. This issue is fixed in 2.18.9, 2.19.7, 2.20.9, 2.21.5, 2.22.4, 2.23.4, and 2.24.10. Note that sandboxing is not enabled by default on macOS. The Nix sandbox is not primarily intended as a security mechanism, but as an aid to improve reproducibility and purity of Nix builds. However, sandboxing can mitigate the impact of other security issues by limiting what parts of the host system a build has access to.

CVE assignment is pending.

Fixes are available, and users are strongly encouraged to upgrade.

For full details (affected versions, fixed releases, mitigations), see:

https://discourse.nixos.org/t/security-advisory-local-privilege-escalation-in-lix-and-nix/77407

Martin