Nix sandbox escape: file write via symlink at FOD `.tmp` copy destination
Summary
| CVE | CVE-2026-39860 |
|---|---|
| State | PUBLISHED |
| Assigner | GitHub_M |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-04-08 21:17:00 UTC |
| Updated | 2026-04-08 21:26:13 UTC |
| 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. |
Risk And Classification
Primary CVSS: v3.1 9 CRITICAL from [email protected]
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Problem Types: CWE-61 | CWE-61 CWE-61: UNIX Symbolic Link (Symlink) Following
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Secondary | 9 | CRITICAL | CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N |
| 3.1 | CNA | DECLARED | 9 | CRITICAL | CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N |
CVSS v3.1 Breakdown
Attack Vector
LocalAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
ChangedConfidentiality
HighIntegrity
HighAvailability
NoneCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | NixOS | Nix | affected >= 2.21, < 2.28.6 | Not specified |
| CNA | NixOS | Nix | affected >= 2.29.0, < 2.29.3 | Not specified |
| CNA | NixOS | Nix | affected >= 2.30.0, < 2.30.4 | Not specified |
| CNA | NixOS | Nix | affected >= 2.31.0, < 2.31.4 | Not specified |
| CNA | NixOS | Nix | affected >= 2.32.0, < 2.32.7 | Not specified |
| CNA | NixOS | Nix | affected >= 2.33.0, < 2.33.4 | Not specified |
| CNA | NixOS | Nix | affected >= 2.34.0, < 2.34.5 | Not specified |
| CNA | NixOS | Nix | affected >= 2.20.5, <= 2.20.9 | Not specified |
| CNA | NixOS | Nix | affected >= 2.19.4, <= 2.19.7 | Not specified |
| CNA | NixOS | Nix | affected >= 2.18.2, <= 2.18.9 | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/NixOS/nix/pull/10178 | [email protected] | github.com | |
| github.com/NixOS/nix/commit/4bc5a3510fa3735798f9ed3a2a30a3ea7b32343a | [email protected] | github.com | |
| github.com/NixOS/nix/commit/a3163b9eabb952b4aa96e376dea95ebcca97b31a | [email protected] | github.com | |
| github.com/NixOS/nix/security/advisories/GHSA-g3g9-5vj6-r3gj | [email protected] | github.com | |
| github.com/NixOS/nix/commit/7794354a982449927ee7401cdeb573ddd16c4688 | [email protected] | github.com | |
| github.com/NixOS/nix/commit/244f3eee0bbc7f11e9b383a15ed7368e2c4becc9 | [email protected] | github.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.