CVE-2026-39860 (GCVE-0-2026-39860)
Vulnerability from cvelistv5 – Published: 2026-04-08 20:58 – Updated: 2026-04-09 13:42
VLAI?
Title
Nix sandbox escape: file write via symlink at FOD `.tmp` copy destination
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.
Severity ?
9 (Critical)
CWE
- CWE-61 - UNIX Symbolic Link (Symlink) Following
Assigner
References
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Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| NixOS | nix |
Affected:
>= 2.21, < 2.28.6
Affected: >= 2.29.0, < 2.29.3 Affected: >= 2.30.0, < 2.30.4 Affected: >= 2.31.0, < 2.31.4 Affected: >= 2.32.0, < 2.32.7 Affected: >= 2.33.0, < 2.33.4 Affected: >= 2.34.0, < 2.34.5 Affected: >= 2.20.5, <= 2.20.9 Affected: >= 2.19.4, <= 2.19.7 Affected: >= 2.18.2, <= 2.18.9 |
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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