Vulnerability · Published Apr 8, 2026 · Assigned by GitHub_M
CVE-2026-39860Nix sandbox escape: file write via symlink at FOD `.tmp` copy destination
Critical 9.0
In plain English
A critical-severity security flaw in nix from NixOS. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 9% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | nix | no fix listed | DEBIAN-CVE-2026-39860 |
| Debian:14 | nix | 2.34.6+dfsg-1 | DEBIAN-CVE-2026-39860 |
| Ubuntu:25.10 | nix | no fix listed | UBUNTU-CVE-2026-39860 |
| Ubuntu:26.04:LTS | nix | no fix listed | UBUNTU-CVE-2026-39860 |
| Ubuntu:26.10 | nix | no fix listed | UBUNTU-CVE-2026-39860 |
Affected products (as reported)
Weakness: CWE-61 · Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
References
- https://github.com/NixOS/nix/security/advisories/GHSA-g3g9-5vj6-r3gj x_refsource_CONFIRM
- https://github.com/NixOS/nix/pull/10178 x_refsource_MISC
- https://github.com/NixOS/nix/commit/244f3eee0bbc7f11e9b383a15ed7368e2c4becc9 x_refsource_MISC
- https://github.com/NixOS/nix/commit/4bc5a3510fa3735798f9ed3a2a30a3ea7b32343a x_refsource_MISC
- https://github.com/NixOS/nix/commit/7794354a982449927ee7401cdeb573ddd16c4688 x_refsource_MISC
- https://github.com/NixOS/nix/commit/a3163b9eabb952b4aa96e376dea95ebcca97b31a x_refsource_MISC