EUVD-2026-63424Severity by source
AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:N
Local-only exploitation via race condition (AC:H), low-privilege derivation submission (PR:L), sandbox escape changes scope (S:C), limited to empty-file creation (I:L), no confidentiality or availability impact.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
Lifecycle Timeline
3DescriptionCVE.org
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.
AnalysisAI
Sandbox escape in Nix versions before 2.35.0 allows a malicious build derivation - executed under the experimental recursive-nix feature - to create or truncate empty files outside the build sandbox using the nix-daemon's permissions by exploiting a TOCTOU race in the LocalStore path-restore logic. The race window exists between path resolution and the open() call with O_TRUNC in writeFile, which previously lacked O_NOFOLLOW enforcement, letting an attacker substitute a symlink mid-flight to redirect the write. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the `recursive-nix` experimental feature to be explicitly enabled in the Nix configuration (`experimental-features = recursive-nix` in `nix.conf` or equivalent), which is off by default and considered experimental. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 score of 2.8 (AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:N) reflects the tightly constrained nature of this vulnerability: local system access is required, the race must be won (AC:H), and the only achievable primitive is creating or zeroing out files - arbitrary content writes are not possible. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade to Nix 2.35.0 or later, which resolves this vulnerability by enforcing `FinalSymlink::DontFollow` through all `writeFile` call sites in the LocalStore restore path, backed by `O_NOFOLLOW` at the syscall level. … Detailed patch versions, workarounds, and compensating controls in full report. |
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Same weakness CWE-61 – UNIX Symbolic Link (Symlink) Following
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External POC / Exploit Code
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