CVE-2026-39860
Nix: symlink abuse in fixed-output derivation allows root overwrite in multi-user builds.
Is CVE-2026-39860 being exploited?
Not confirmed. CVE-2026-39860 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.19% probability of exploitation in the next 30 days.
How severe is CVE-2026-39860?
CVE-2026-39860 is rated Critical with a CVSS score of 9.0. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-39860?
Yes. A fix has been recorded for CVE-2026-39860. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-39860 affect?
CVE-2026-39860 affects Nix package manager (multi-user installs), Linux/Unix hosts running Nix daemon. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-39860?
Upgrade Nix to fixed versions (2.34.5+), across multi-user hosts
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Root escalation via arbitrary file overwrite by following symlinks during output registration in multi-user Nix builds.
Patch when possible
- affected>= 2.21 and < 2.28.6
- affected>= 2.29.0 and < 2.29.3
- affected>= 2.30.0 and < 2.30.4
- affected>= 2.31.0 and < 2.31.4
- affected>= 2.32.0 and < 2.32.7
- affected>= 2.33.0 and < 2.33.4
- affected>= 2.34.0 and < 2.34.5
- affected>= 2.20.5 and <= 2.20.9
- affected>= 2.19.4 and <= 2.19.7
- affected>= 2.18.2 and <= 2.18.9
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.