Root privilege escalation via symlink-following output copy
Published Apr 8, 2026 · Updated Apr 8, 2026
Privilege escalation in affected Nix releases allows local users to gain root access through a malicious fixed-output derivation. During output registration, LocalDerivationGoal::registerOutputs copies the derivation output to an actualPath + ".tmp" destination inside the build chroot, then the host-side Nix process follows a builder-created symlink and overwrites its target. Sandboxed Linux multi-user installations are affected when users can submit builds to the daemon; sandboxed macOS builds are unaffected.
Summary
What happened
Privilege escalation in affected Nix releases allows local users to gain root access through a malicious fixed-output derivation. During output registration, LocalDerivationGoal::registerOutputs copies the derivation output to an actualPath + ".tmp" destination inside the build chroot, then the host-side Nix process follows a builder-created symlink and overwrites its target. Sandboxed Linux multi-user installations are affected when users can submit builds to the daemon; sandboxed macOS builds are unaffected.
The record
- CVE
- CVE-2026-39860
- Published
- Apr 8, 2026
- Updated
- Apr 8, 2026
- Vendor
- NixOS
- Product
- Nix
- Classifications
- CWE-61, T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Apr 8, 2026CVE publishedPublication date reported by the CVE source.
- Apr 8, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=>= 2.18.2, <= 2.18.9
- Affected versionversion=>= 2.19.4, <= 2.19.7
- Affected versionversion=>= 2.20.5, <= 2.20.9
- Affected versionversion=>= 2.21, < 2.28.6
- Affected versionversion=>= 2.29.0, < 2.29.3
- Affected versionversion=>= 2.30.0, < 2.30.4
- Affected versionversion=>= 2.31.0, < 2.31.4
- Affected versionversion=>= 2.32.0, < 2.32.7
- Affected versionversion=>= 2.33.0, < 2.33.4
- Affected versionversion=>= 2.34.0, < 2.34.5
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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