CVE-2026-64846: CWE-61: UNIX Symbolic Link (Symlink) Following in NixOS nix
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.
CVSS v3.1
Score 2.8low
Affected software
NixOS
nix
Run on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Nix versions before 2.35.0 contain a race condition vulnerability (CVE-2026-64846) related to symbolic link following in the LocalStore restore path when using the recursive-nix experimental feature. Specifically, a time-of-check/time-of-use race allows writeFile to follow a substituted final symlink with O_TRUNC, bypassing the intended FinalSymlink::DontFollow enforcement. This can lead to the creation or truncation of an empty file outside the build sandbox with the permissions of the nix-daemon user. The vulnerability does not permit arbitrary content writes and requires successfully winning the race condition. The flaw is addressed in version 2.35.0.
Potential Impact
An attacker who can execute a malicious derivation with the recursive-nix experimental feature enabled may exploit this race condition to create or truncate files outside the build sandbox with the nix-daemon user's permissions. This could potentially affect system integrity by modifying files unexpectedly. However, the vulnerability does not allow arbitrary content writes, limiting the scope of impact. The low CVSS score (2.8) reflects the limited impact and the complexity of exploitation.
Mitigation Recommendations
Upgrade to Nix version 2.35.0 or later, where this vulnerability is fixed. No other mitigation is indicated or required according to the available data.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-07-20T18:31:39.290Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6a872d7aacd9273b49dd41d8
Added to database: 08/20/2026, 16:38:18 UTC
Last enriched: 08/20/2026, 16:52:49 UTC
Last updated: 10/04/2026, 18:53:17 UTC
Views: 85
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.