CVE-2026-39860

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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."}, {"lang": "es", "value": "Nix es un gestor de paquetes para Linux y otros sistemas Unix. Un error en la correcci\u00f3n para CVE-2024-27299 permiti\u00f3 sobrescrituras arbitrarias de archivos escribibles por el proceso Nix que orquesta las compilaciones (t\u00edpicamente el demonio Nix ejecut\u00e1ndose como root en instalaciones multiusuario) al seguir enlaces simb\u00f3licos durante el registro de salida de derivaciones de salida fija. Esto afecta a las compilaciones de Linux en entornos aislados; las compilaciones de macOS en entornos aislados no se ven afectadas. La ubicaci\u00f3n de la salida temporal utilizada para la copia de salida se encontraba dentro del chroot de compilaci\u00f3n. Un enlace simb\u00f3lico, apuntando a una ubicaci\u00f3n arbitraria en el sistema de archivos, podr\u00eda ser creado por el constructor de la derivaci\u00f3n en esa ruta. Durante el registro de salida, el proceso Nix (ejecut\u00e1ndose en el espacio de nombres de montaje del host) seguir\u00eda ese enlace simb\u00f3lico y sobrescribir\u00eda el destino con el contenido de salida de la derivaci\u00f3n. En instalaciones multiusuario, esto permite a todos los usuarios capaces de enviar compilaciones al demonio Nix (usuarios permitidos - por defecto todos los usuarios) obtener privilegios de root modificando archivos sensibles. Esta vulnerabilidad est\u00e1 corregida en 2.34.5, 2.33.4, 2.32.7, 2.31.4, 2.30.4, 2.29.3 y 2.28.6."}], "id": "CVE-2026-39860", "lastModified": "2026-07-24T21:10:00.143", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "NONE", "baseScore": 9.0, "baseSeverity": "CRITICAL", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "NONE", "scope": "CHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N", "version": "3.1"}, "exploitabilityScore": 2.5, "impactScore": 5.8, "source": "security-advisories@github.com", "type": "Secondary"}, {"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "NONE", "baseScore": 8.4, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "LOW", "scope": "CHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N", "version": "3.1"}, "exploitabilityScore": 2.0, "impactScore": 5.8, "source": "nvd@nist.gov", "type": "Primary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-39860", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "total"}], "role": "CISA Coordinator", "timestamp": "2026-04-09T13:42:26.389636Z", "version": "2.0.3"}}]}, "published": "2026-04-08T21:17:00.157", "references": [{"source": "security-advisories@github.com", "tags": ["Patch"], "url": "https://github.com/NixOS/nix/commit/244f3eee0bbc7f11e9b383a15ed7368e2c4becc9"}, {"source": "security-advisories@github.com", "tags": ["Patch"], "url": "https://github.com/NixOS/nix/commit/4bc5a3510fa3735798f9ed3a2a30a3ea7b32343a"}, {"source": "security-advisories@github.com", "tags": ["Patch"], "url": "https://github.com/NixOS/nix/commit/7794354a982449927ee7401cdeb573ddd16c4688"}, {"source": "security-advisories@github.com", "tags": ["Patch"], "url": "https://github.com/NixOS/nix/commit/a3163b9eabb952b4aa96e376dea95ebcca97b31a"}, {"source": "security-advisories@github.com", "tags": ["Issue Tracking", "Patch"], "url": "https://github.com/NixOS/nix/pull/10178"}, {"source": "security-advisories@github.com", "tags": ["Mitigation", "Patch", "Vendor Advisory"], "url": "https://github.com/NixOS/nix/security/advisories/GHSA-g3g9-5vj6-r3gj"}], "sourceIdentifier": "security-advisories@github.com", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-61"}], "source": "security-advisories@github.com", "type": "Secondary"}]}

{}

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