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CVE-2026-39860

Nixos Nix vulnerability

9.0 CRITICALEPSS 0.18%
  1. Published8 Apr 2026

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.

CVSS 3.1 breakdown

Attack vectorLocal
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeChanged
ConfidentialityHigh
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

Affected products

Nixos Nix≥ 2.18.2 ≤ 2.18.9 · ≥ 2.19.4 ≤ 2.19.7 · ≥ 2.20.5 ≤ 2.20.9 · ≥ 2.21.0 < 2.28.6

Remediation

Fixed in
Nixos Nix≥ 2.28.6

References

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Frequently asked

Is CVE-2026-39860 being actively exploited?

CVE-2026-39860 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.18%.

How severe is CVE-2026-39860?

CVE-2026-39860 has a CVSS 3.1 base score of 9.0, rated critical. EPSS estimates a 0.18% probability of exploitation.

Which products are affected by CVE-2026-39860?

Affected products include Nixos Nix.

How do I fix CVE-2026-39860?

Upgrade affected software to a fixed version, for example Nixos Nix 2.28.6 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-39860 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.