CVE-2025-54864 is a vulnerability identified in the NixOS hydra continuous integration (CI) service, specifically affecting versions prior to commit f7bda02. Hydra is used to automate builds and evaluations for Nix-based projects. The vulnerability arises from missing authentication controls on two critical API endpoints: /api/push-github and /api/push-gitea. These endpoints are designed to be called by their respective forges (GitHub and Gitea) to trigger evaluations. However, before the patch, these endpoints did not enforce HTTP Basic authentication, relying solely on HMAC signing with a secret key for verification. This lack of robust authentication means that an attacker could potentially invoke these endpoints without proper credentials, triggering resource-intensive evaluations. Such forced evaluations can impose significant load on the infrastructure, potentially leading to denial of service (DoS) conditions on the host running the evaluator. The vulnerability is classified under CWE-306, indicating missing authentication for a critical function. The issue has been addressed in commit f7bda02, which introduced proper authentication mechanisms. As an interim mitigation, blocking access to these endpoints via a reverse proxy is recommended. The CVSS 4.0 base score is 6.9 (medium severity), reflecting the network attack vector, low attack complexity, no privileges or user interaction required, and limited impact on availability. No known exploits are currently reported in the wild. This vulnerability highlights the risk of insufficient authentication in CI/CD pipelines, which can be exploited to disrupt development workflows and infrastructure stability.

For European organizations utilizing NixOS hydra for continuous integration, this vulnerability poses a risk of service disruption through denial of service attacks. Since triggering evaluations can be resource-intensive, an attacker exploiting this flaw could degrade or halt CI operations, impacting software development lifecycles and potentially delaying critical updates or deployments. This is particularly significant for organizations in sectors with stringent compliance and rapid release requirements, such as finance, healthcare, and critical infrastructure. Additionally, if the CI environment is integrated with production deployment pipelines, disruption could cascade, affecting operational systems. The lack of authentication also raises concerns about unauthorized triggering of builds, which could be leveraged for supply chain attacks or to introduce malicious code if combined with other vulnerabilities. However, the absence of known exploits and the medium severity rating suggest that while impactful, the threat is currently limited in scope. Organizations with large-scale or heavily automated Nix-based development environments are at higher risk due to the potential scale of resource exhaustion.

1. Immediate patching: Upgrade NixOS hydra to the version including commit f7bda02 or later, which implements proper authentication on the /api/push-github and /api/push-gitea endpoints. 2. Reverse proxy controls: Until patching is possible, configure reverse proxies or firewalls to block or restrict access to these API endpoints, allowing only trusted forge IP addresses or networks. 3. HMAC secret management: Ensure that HMAC secrets used for signing requests are securely generated, stored, and rotated regularly to prevent unauthorized use. 4. Monitoring and alerting: Implement monitoring on API usage patterns to detect unusual or excessive evaluation triggers that could indicate exploitation attempts. 5. Rate limiting: Apply rate limiting on the vulnerable endpoints to reduce the risk of resource exhaustion from repeated calls. 6. Access control review: Conduct a comprehensive review of authentication and authorization mechanisms across CI/CD infrastructure to prevent similar issues. 7. Incident response readiness: Prepare response plans for potential DoS incidents affecting CI services to minimize operational impact.