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.

Affected products

Nix

Nixos Nix

≤ 2.18.9, 2.19.7, 2.20.9, 2.28.6, 2.29.3, 2.30.4, 2.31.4, 2.32.7, 2.33.4, 2.34.5

Fix

Available

CVSS 3.1

9.0 CRITICAL

EPSS

0.2% (9th percentile)

Weakness

CWE-61

NVD status

Analyzed

Published

2026-04-08

No exploit for CVE-2026-39860 has been indexed yet. Our index is built from live traffic and upstream syncs, so this page can only say what it knows — not that no exploit exists.