Nix: Arbitrary file truncation outside the sandbox with recursive-nix experimental feature

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Summary

CVECVE-2026-64846
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-20 17:19:16 UTC
Updated2026-08-20 20:17:45 UTC
DescriptionNix 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.

Risk And Classification

Primary CVSS: v3.1 2.8 LOW from [email protected]

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:N

EPSS: 0.000870000 probability, percentile 0.004390000 (date 2026-08-21)

Problem Types: CWE-61 | CWE-367 | CWE-61 CWE-61: UNIX Symbolic Link (Symlink) Following | CWE-367 CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary2.8LOWCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:N
3.1CNADECLARED2.8LOWCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Changed
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA NixOS Nix affected < 2.35.0 Not specified

References

ReferenceSourceLinkTags
github.com/NixOS/nix/commit/26679828f74ee6e82a4100904e6361f993ff5390 [email protected] github.com
github.com/NixOS/nix/pull/15401 [email protected] github.com
github.com/NixOS/nix/security/advisories/GHSA-6h4g-g5j9-fm5f [email protected] github.com
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