Vulnerability · Published Aug 20, 2026 · Assigned by GitHub_M
CVE-2026-64846Nix: Arbitrary file truncation outside the sandbox with recursive-nix experimental feature
Low 2.8
In plain English
A low-severity security flaw in nix from NixOS. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 1% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | nix | no fix listed | DEBIAN-CVE-2026-64846 |
| Debian:13 | nix | no fix listed | DEBIAN-CVE-2026-64846 |
| Debian:14 | nix | 2.35.4+dfsg-1 | DEBIAN-CVE-2026-64846 |
| Ubuntu:26.04:LTS | nix | no fix listed | UBUNTU-CVE-2026-64846 |
| Ubuntu:26.10 | nix | no fix listed | UBUNTU-CVE-2026-64846 |
Affected products (as reported)
Weakness: CWE-61, CWE-367 · Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:N
References
- https://github.com/NixOS/nix/security/advisories/GHSA-6h4g-g5j9-fm5f x_refsource_CONFIRM
- https://github.com/NixOS/nix/pull/15401 x_refsource_MISC
- https://github.com/NixOS/nix/commit/26679828f74ee6e82a4100904e6361f993ff5390 x_refsource_MISC