CVE-2026-39860

CRITICALNVD 9.09.0—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.0 under NVD CVSS v3. EPSS exploit probability: 0.0%, top 98% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
9.0
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 0%CVSS: 9.0Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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 v3
9.0
EG Score
9.0(medium)
EG Risk
—
EPSS
9.3%
KEV
Not listed

Published

April 8, 2026

Last Modified

April 15, 2026

Advisory Details (6)

Auto-updated May 22, 2026
Patch available. Sources: github.
github Patch Available

Sandbox escape: file write via symlink at FOD `.tmp` copy destination · Advisory · NixOS/nix · GitHub

Affected: 2.34.5, 2.33.4, 2.32.7, 2.31.4, 2.30.4, 2.29.3, 2.28.6. The temporary output copy

https://github.com/NixOS/nix/security/advisories/GHSA-g3g9-5vj6-r3gj
generic

Fix the outputs moving on macOS by thufschmitt · Pull Request #10178 · NixOS/nix · GitHub

https://github.com/NixOS/nix/pull/10178
generic

Fix the outputs moving on macOS · NixOS/nix@a3163b9 · GitHub

https://github.com/NixOS/nix/commit/a3163b9eabb952b4aa96e376dea95ebcca97b31a
generic

Fix sandbox escape patch · NixOS/nix@7794354 · GitHub

https://github.com/NixOS/nix/commit/7794354a982449927ee7401cdeb573ddd16c4688
generic

Copy the output of fixed-output derivations before registering them · NixOS/nix@4bc5a35 · GitHub

https://github.com/NixOS/nix/commit/4bc5a3510fa3735798f9ed3a2a30a3ea7b32343a
generic

Copy the output of fixed-output derivations before registering them · NixOS/nix@244f3ee · GitHub

https://github.com/NixOS/nix/commit/244f3eee0bbc7f11e9b383a15ed7368e2c4becc9

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 8× in last 7d / 33× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-22 14:08 UTCEPSS rescore
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  3. 2026-07-20 21:02 UTCOSV refresh
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  1. 2026-06-29 14:06 UTCEPSS rescore
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  62. 2026-05-20 18:15 UTCEG score recompute
  63. 2026-05-20 11:22 UTCEPSS rescore
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Frequently asked(5)

What is CVE-2026-39860?
CVE-2026-39860 is a critical vulnerability published on April 8, 2026. 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…
When was CVE-2026-39860 disclosed?
CVE-2026-39860 was first published in the National Vulnerability Database on April 8, 2026, with the most recent update on April 15, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-39860 actively exploited?
CVE-2026-39860 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 9.3% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-39860?
CVE-2026-39860 has a CVSS v3 base score of 9.0 (NVD).
How do I remediate CVE-2026-39860?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-39860, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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