CVE-2026-39860: Nix is a package manager for Linux and other Unix systems. A bug in the fix for CVE-2024-27297 allowed for arbitrary overwrites of files writable by t...

Description

Nix is a package manager for Linux and other Unix systems. A bug in the fix for CVE-2024-27297 allowed for arbitrary overwrites of files writable by the Nix process orchestrating the builds (typically the Nix daemon running as root in multi-user installations) by following symlinks during fixed-output derivation output registration. This affects sandboxed Linux builds - sandboxed macOS builds are unaffected. The location of the temporary output used for the output copy was located inside the build chroot. A symlink, pointing to an arbitrary location in the filesystem, could be created by the derivation builder at that path. During output registration, the Nix process (running in the host mount namespace) would follow that symlink and overwrite the destination with the derivation's output contents. In multi-user installations, this allows all users able to submit builds to the Nix daemon (allowed-users - defaulting to all users) to gain root privileges by modifying sensitive files. This vulnerability is fixed in 2.34.5, 2.33.4, 2.32.7, 2.31.4, 2.30.4, 2.29.3, and 2.28.6.

Metrics

CVSS 3.1

8.4/10

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

EPSS Probability

0.19%

9.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-61

Affected Software

Vendor	Product	Versions
Nixos	Nix	>= 2.18.2, <= 2.18.9
Nixos	Nix	>= 2.19.4, <= 2.19.7
Nixos	Nix	>= 2.20.5, <= 2.20.9
Nixos	Nix	>= 2.21.0, < 2.28.6
Nixos	Nix	>= 2.29.0, < 2.29.3
Nixos	Nix	>= 2.30.0, < 2.30.4
Nixos	Nix	>= 2.31.0, < 2.31.4
Nixos	Nix	>= 2.32.0, < 2.32.7
Nixos	Nix	>= 2.33.0, < 2.33.4
Nixos	Nix	>= 2.34.0, < 2.34.5

References

https://github.com/NixOS/nix/commit/244f3eee0bbc7f11e9b383a15ed7368e2c4becc9Patch
https://github.com/NixOS/nix/commit/4bc5a3510fa3735798f9ed3a2a30a3ea7b32343aPatch
https://github.com/NixOS/nix/commit/7794354a982449927ee7401cdeb573ddd16c4688Patch
https://github.com/NixOS/nix/commit/a3163b9eabb952b4aa96e376dea95ebcca97b31aPatch
https://github.com/NixOS/nix/pull/10178Issue Tracking, Patch
https://github.com/NixOS/nix/security/advisories/GHSA-g3g9-5vj6-r3gjMitigation, Patch, Vendor Advisory

Timeline

Published: Apr 8, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-39860?

Nix is a package manager for Linux and other Unix systems. A bug in the fix for CVE-2024-27297 allowed for arbitrary overwrites of files writable by the Nix process orchestrating the builds (typically the Nix daemon running as root in multi-user installations) by following symlinks during fixed-output derivation output registration. This affects sandboxed Linux builds - sandboxed macOS builds are unaffected. The location of the temporary output used for the output copy was located inside the build chroot. A symlink, pointing to an arbitrary location in the filesystem, could be created by the derivation builder at that path. During output registration, the Nix process (running in the host mount namespace) would follow that symlink and overwrite the destination with the derivation's output contents. In multi-user installations, this allows all users able to submit builds to the Nix daemon (allowed-users - defaulting to all users) to gain root privileges by modifying sensitive files. This vulnerability is fixed in 2.34.5, 2.33.4, 2.32.7, 2.31.4, 2.30.4, 2.29.3, and 2.28.6.

How severe is CVE-2026-39860?

CVE-2026-39860 has a CVSS score of 8.4/10 (HIGH severity). The EPSS model estimates a 0.19% probability of exploitation in the next 30 days.

How do I fix CVE-2026-39860?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.