UNIX Symbolic Link (Symlink) Following in nix - CVE-2026-39860
Published: April 8, 2026 / Updated: April 9, 2026
Vulnerability identifier: #VU125379
CSH Severity: Low
CVSS v4.0: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear
CVE-ID: CVE-2026-39860
CWE-ID: CWE-61
Exploitation vector: Local access
Exploit availability:
No public exploit available
Vendor: nixos.org
Affected software:
nix
nix
Detailed vulnerability description
The vulnerability allows a remote attacker to escalate privileges.
The vulnerability exists due to unix symbolic link following in fixed-output derivation output registration when copying temporary fixed-output derivation outputs from the build chroot. A remote attacker can create a symlink at the temporary output path to overwrite arbitrary writable files and escalate privileges.
This affects sandboxed Linux builds, while sandboxed macOS builds are unaffected.
How to mitigate CVE-2026-39860
Install security update from vendor's website.