CVE-2026-39860: Nix is a package manager for Linux and other Unix systems

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CRITICAL 9.0WATCHLISTUPGRADE

CVE-2026-39860 is a critical-severity flaw (CVSS 9.0) affecting nix. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 u

Why this priority

Critical severity
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.0 (Critical)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.2% (top 91%)
CISA exploited list	No
Weakness	CWE-61
Published	2026-04-08
Last modified	2026-07-24

Publisher (CNA): GitHub, Inc. · Vendor: nixos

Last updated 2026-07-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-08 21:17 UTCPublished CVE record published
2026-07-24 21:10 UTCUpdated Record last modified

nixos nix UPGRADE

Affected: >= 2.18.2 and <= 2.18.9 · >= 2.19.4 and <= 2.19.7 · >= 2.20.5 and <= 2.20.9 · >= 2.21.0 and < 2.28.6 · >= 2.29.0 and < 2.29.3 · >= 2.30.0 and < 2.30.4 · >= 2.31.0 and < 2.31.4 · >= 2.32.0 and < 2.32.7

Fixed in: 2.28.6, 2.29.3, 2.30.4, 2.31.4, 2.32.7, 2.33.4, 2.34.5

Safe to downgrade to: a release before 2.18.2

1. Check installed version

apt-cache policy nix || rpm -q nix || nix --version

2. UPGRADE to 2.28.6 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade nix

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade nix

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 2.18.2 (Debian / Ubuntu)

apt-cache madison nix sudo apt install nix=<VERSION_BEFORE_2.18.2> sudo apt-mark hold nix

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list nix sudo dnf downgrade nix-<VERSION_BEFORE_2.18.2> sudo dnf versionlock add nix

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-39860?

nix: upgrade to 2.28.6, 2.29.3, 2.30.4, 2.31.4, 2.32.7, 2.33.4, 2.34.5. Exact commands for each OS are on this page.

Is CVE-2026-39860 being exploited?

CVE-2026-39860 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-39860 affect?

CVE-2026-39860 affects nix. Severity is critical (CVSS 9.0). 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

How urgent is CVE-2026-39860?

Priority 39/100. Critical severity; On your watchlist

Software pages

macOS vulnerabilities

References

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