CVE-2025-32435 in Hydra
Summary
by MITRE • 04/16/2025
Hydra is a Continuous Integration service for Nix based projects. Evaluation of untrusted non-flake nix code could potentially access secrets that are accessible by the hydra user/group. This should not affect the signing keys, that are owned by the hydra-queue-runner and hydra-www users respectively.
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Analysis
by VulDB Data Team • 04/16/2025
The vulnerability identified as CVE-2025-32435 affects Hydra, a continuous integration service specifically designed for Nix-based projects. This system operates by evaluating Nix expressions and configurations to automate build processes and maintain software repositories. The flaw resides in how Hydra handles the evaluation of untrusted non-flake Nix code, creating a potential security escalation path that could allow malicious code execution with elevated privileges. The vulnerability specifically impacts the security boundaries between different user contexts within the Hydra service architecture, where code evaluation processes run under the hydra user/group permissions.
The technical implementation of this vulnerability stems from insufficient sandboxing and privilege separation during the evaluation of Nix expressions. When Hydra processes untrusted code, it fails to properly isolate the execution environment from the underlying system resources that are accessible to the hydra user account. This creates an attack surface where malicious Nix code could potentially access sensitive system resources, configuration files, or environment variables that are accessible through the hydra user context. The vulnerability is particularly concerning because Nix expressions can contain complex logic that might exploit path traversal, file system access, or environment variable manipulation to bypass normal security controls. According to CWE classification, this represents a weakness in privilege management and sandboxing controls, specifically CWE-276 for insecure file permissions and CWE-250 for execution with unnecessary privileges.
The operational impact of this vulnerability extends beyond simple code execution, as it could enable attackers to access sensitive information that might be stored in the Hydra environment. While the description notes that signing keys remain protected since they are owned by dedicated hydra-queue-runner and hydra-www users, the broader system security posture is compromised. Attackers could potentially extract build secrets, access internal configuration data, or manipulate the build environment to inject malicious artifacts into the continuous integration pipeline. This could lead to supply chain compromises where trusted builds are contaminated with malicious code, affecting downstream consumers of the software artifacts. The vulnerability also represents a potential escalation path from a code injection attack to a more significant compromise of the entire CI/CD infrastructure, as demonstrated in ATT&CK framework under techniques related to privilege escalation and credential access.
Mitigation strategies should focus on implementing stricter sandboxing mechanisms during Nix code evaluation, ensuring proper privilege separation between different Hydra service components, and limiting the access rights of the hydra user account to only essential system resources. Organizations should implement mandatory access controls, use dedicated execution environments with reduced privileges, and consider implementing additional code analysis layers that can detect and block potentially malicious Nix expressions before they are evaluated. Regular security audits of the Hydra configuration and access controls should be conducted, along with monitoring for unauthorized access attempts or unusual file system activity during build processes. The implementation of defense-in-depth strategies including network segmentation, process monitoring, and automated vulnerability scanning can help detect and prevent exploitation attempts. Additionally, maintaining up-to-date Hydra installations and following security best practices for Nix-based systems will reduce the overall risk exposure while ensuring continued compliance with security standards and regulatory requirements.