CVE-2025-46416 is a vulnerability classified under CWE-282 (Improper Ownership Management) affecting the NixOS ecosystem's package managers: Nix, Lix, and Guix. These package managers are designed to provide reproducible and isolated build environments. The vulnerability allows a user to bypass build isolation mechanisms, enabling privilege escalation to the build user account (such as nixbld or guixbuild). This means that a non-privileged user can gain the privileges of the build user, which typically has elevated rights within the build environment. The affected versions include Nix up to 2.29.1 (specifically versions 0, 2.25.0, 2.27.0, and 2.29.0), Lix up to 2.93.1, and Guix before 1.4.0-38.0e79d5b. The vulnerability arises due to improper management of ownership and permissions during the build process, allowing unauthorized access to build user privileges. Although the CVSS score is low (2.9), indicating limited impact and difficulty of exploitation, the flaw undermines the isolation guarantees that these package managers provide, potentially allowing attackers to interfere with build processes or access sensitive build artifacts. No known exploits are reported in the wild, and no patches are linked, suggesting that mitigation may require updating to fixed versions once available or applying vendor guidance. The attack vector is local (AV:L), requiring local access with no privileges (PR:N), no user interaction (UI:N), and high attack complexity (AC:H). The impact is limited to integrity (I:L) with no confidentiality or availability impact.

For European organizations, especially those relying on NixOS, Nix, Lix, or Guix package managers for software builds and deployments, this vulnerability could compromise the integrity of the build environment. Attackers with local access could escalate privileges within the build system, potentially injecting malicious code into software builds or tampering with build artifacts. This could lead to supply chain risks, where compromised builds propagate malware or backdoors into production systems. Although the vulnerability does not directly affect confidentiality or availability, the integrity breach could have downstream effects on software trustworthiness and compliance with European cybersecurity regulations such as the NIS Directive and GDPR if compromised software leads to data breaches. Organizations using these package managers in CI/CD pipelines or development environments should be aware of the risk of local privilege escalation and the potential for insider threats or compromised developer machines to impact software supply chain security.

1. Upgrade to patched versions of Nix, Lix, and Guix as soon as they become available from the respective maintainers. Monitor official channels for security advisories and patches. 2. Restrict local access to build environments and package managers to trusted users only, minimizing the risk of unprivileged users exploiting this vulnerability. 3. Implement strict access controls and auditing on build user accounts (e.g., nixbld, guixbuild) to detect unauthorized privilege escalations. 4. Use containerization or virtualization to further isolate build environments, reducing the impact of privilege escalation within the build user context. 5. Employ integrity verification mechanisms such as reproducible builds and cryptographic signing of build artifacts to detect tampering. 6. Regularly review and harden build environment configurations to ensure ownership and permission settings follow the principle of least privilege. 7. Educate developers and build engineers about the risks of local privilege escalation and enforce policies to prevent unauthorized local access to build systems.