CVE-2026-64846: CWE-61: UNIX Symbolic Link (Symlink) Following in NixOS nix
CVE-2026-64846 is a low-severity vulnerability in the Nix package manager prior to version 2.35.0. It involves a time-of-check/time-of-use race condition in the handling of symbolic links during the LocalStore restore path when the recursive-nix experimental feature is enabled. This race condition can cause the nix process or nix-daemon to create or truncate an empty file outside the build sandbox with the daemon user's permissions. The vulnerability does not allow arbitrary content writes and requires winning the race to exploit. The issue is fixed in Nix version 2.35.0.
AI Analysis
Technical Summary
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.
CVE-2026-64846: CWE-61: UNIX Symbolic Link (Symlink) Following in NixOS nix
Description
CVE-2026-64846 is a low-severity vulnerability in the Nix package manager prior to version 2.35.0. It involves a time-of-check/time-of-use race condition in the handling of symbolic links during the LocalStore restore path when the recursive-nix experimental feature is enabled. This race condition can cause the nix process or nix-daemon to create or truncate an empty file outside the build sandbox with the daemon user's permissions. The vulnerability does not allow arbitrary content writes and requires winning the race to exploit. The issue is fixed in Nix version 2.35.0.
CVSS v3.1
Score 2.8low
Affected software
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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
- Remediation Level
- null
Threat ID: 6a872d7aacd9273b49dd41d8
Added to database: 08/20/2026, 16:38:18 UTC
Last enriched: 08/20/2026, 16:52:49 UTC
Last updated: 08/20/2026, 16:52:49 UTC
Views: 4
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