CVE-2026-44029

A bug in the fix for CVE-2024-27297 in Nix allows arbitrary overwrites of files writable by the Nix process by following symlinks during fixed-output derivation output registration. This affects sandboxed Linux builds only.

Nix before 2.35.3, when unsandboxed on macOS or FreeBSD, incorrectly allows connections made by build users from daemon clients.

The multi-user installer in Nix before 2.35.3 sets the ownership of store contents to the user who invoked the installer, even though it should be root ownership.

Nix before 2.35.3 and Lix before 2.95.4 on macOS allow a Seatbelt sandbox escape (for an unconfined build) because a certain size threshold is mishandled.

Nix before 2.35.3 and Lix before 2.95.4 allow privilege escalation via a repair operation that could destroy and then replace a store path before content verification.

Nix before 2.35.3 and Lix before 2.95.4 have an integer overflow and resultant out-of-bounds write when evaluating untrusted expressions because list allocation is mishandled. This can lead to memory corruption and potential code execution.

Nix is a package manager for Linux and other Unix systems. Prior to 2.35.0, a malicious derivation executed with the recursive-nix experimental feature can exploit a time-of-check/time-of-use race involving final symlink handling in the LocalStore restore path. The race can cause writeFile to follow a substituted final symlink when opening a path with O_TRUNC instead of enforcing FinalSymlink::DontFollow, allowing the Nix process or nix-daemon to create or truncate an empty file outside the build sandbox with the daemon user's permissions. The primitive does not provide arbitrary-content writes and requires winning the race. This issue is fixed in version 2.35.0.