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TI-2026-28741 Aliases CVE-2026-39860

Nix sandbox escape: file write via symlink at FOD `.tmp` copy destination

Priority MEDIUM 40CWE-61Published · Updated

Key facts

Attack vector
Local
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
High · High · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00197 9th percentileScored 2026-11-07
Fix Fixed nix (NixOS): 2.28.6, 2.29.3, 2.30.4 +4

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
NixOSnix2.21 to before 2.28.6; 2.29.0 to before 2.29.3; 2.30.0 to before 2.30.4; 2.31.0 to before 2.31.4; 2.32.0 to before 2.32.7; 2.33.0 to before 2.33.4; 2.34.0 to before 2.34.5; 2.20.5 – 2.20.9; 2.19.4 – 2.19.7; 2.18.2 – 2.18.92.28.6, 2.29.3, 2.30.4, 2.31.4, 2.32.7, 2.33.4, 2.34.5Patch availableCNA
  • nix VendorNixOS Affected 2.21 to before 2.28.6; 2.29.0 to before 2.29.3; 2.30.0 to before 2.30.4; 2.31.0 to before 2.31.4; 2.32.0 to before 2.32.7; 2.33.0 to before 2.33.4; 2.34.0 to before 2.34.5; 2.20.5 – 2.20.9; 2.19.4 – 2.19.7; 2.18.2 – 2.18.9 Fixed in 2.28.6, 2.29.3, 2.30.4, 2.31.4, 2.32.7, 2.33.4, 2.34.5 Patch available CNA

CPE configurations NVD · 2

CPEVersionsRoleVendor
cpe:2.3:a:nixos:nix:*:*:*:*:*:*:*:*2.18.2 – 2.18.9; 2.19.4 – 2.19.7; 2.20.5 – 2.20.9; 2.21.0 to before 2.28.6; 2.29.0 to before 2.29.3; 2.30.0 to before 2.30.4; 2.31.0 to before 2.31.4; 2.32.0 to before 2.32.7; 2.33.0 to before 2.33.4; 2.34.0 to before 2.34.5VulnerableNixOS
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:*not specified by NVDRunning onLinux
  • cpe:2.3:a:nixos:nix:*:*:*:*:*:*:*:* Versions 2.18.2 – 2.18.9; 2.19.4 – 2.19.7; 2.20.5 – 2.20.9; 2.21.0 to before 2.28.6; 2.29.0 to before 2.29.3; 2.30.0 to before 2.30.4; 2.31.0 to before 2.31.4; 2.32.0 to before 2.32.7; 2.33.0 to before 2.33.4; 2.34.0 to before 2.34.5 Vulnerable ·NixOS
  • cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* Versions not specified by NVD Running on ·Linux

Remediation

  • Fix · CNA nix (NixOS) Fixed in 2.28.6, 2.29.3, 2.30.4, 2.31.4, 2.32.7, 2.33.4, 2.34.5

Vendor assessments

Red Hat

Red Hat's page for this CVE →

Not affected: 1 product
  • Red Hat

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-39860

References

Patch 6

  • TI-2024-30614 Nix affected by unsafe NAR unpacking CVSS 3.1CRITICAL 9.1
  • TI-2019-12962 Nix through 2.3 allows local users to gain access to an arbitrary user's account because… CVSS 3.1HIGH 7.8
  • TI-2024-18135 Nix Corruption of fixed-output derivations CVSS 3.1MEDIUM 6.3

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences