CVE-2025-54864 in hydra
Summary
by MITRE • 08/12/2025
Hydra is a continuous integration service for Nix based projects. Prior to commit f7bda02, /api/push-github and /api/push-gitea are called by the corresponding forge without HTTP Basic authentication. Both forges do however feature HMAC signing with a secret key. Triggering an evaluation can be very taxing on the infrastructure when large evaluations are done, introducing potential denial of service attacks on the host running the evaluator. This issue has been patched by commit f7bda02. A workaround involves blocking /api/push-github and /api/push-gitea via a reverse proxy.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 08/12/2025
The vulnerability described in CVE-2025-54864 affects Hydra, a continuous integration service specifically designed for Nix-based projects. This service operates as a critical component in automated build and evaluation processes for software projects that rely on the Nix package manager ecosystem. The flaw manifests in the authentication mechanisms for two specific API endpoints: /api/push-github and /api/push-gitea which are utilized by GitHub and Gitea forge integrations respectively. These endpoints were initially configured without HTTP Basic authentication requirements, creating a significant security gap in the system's access control framework.
The technical implementation of this vulnerability stems from the absence of proper authentication mechanisms for these critical API endpoints despite the presence of HMAC signing capabilities within the forge systems themselves. The forges do implement HMAC signing using secret keys for message authentication, but this security measure alone is insufficient when combined with the lack of basic authentication at the Hydra service level. This dual-layer failure creates an exploitable condition where unauthorized parties can potentially submit push notifications to these endpoints without proper credentials, even though the forge systems themselves should be validating the authenticity of incoming requests through their HMAC mechanisms.
The operational impact of this vulnerability extends beyond simple access control violations to encompass potential denial of service scenarios that could severely impact system availability. When large evaluations are triggered through these endpoints, the infrastructure resources required to process these requests become substantial, creating an attack surface where malicious actors could exploit the vulnerability to flood the system with resource-intensive evaluation requests. This creates a scenario where legitimate users might experience service degradation or complete unavailability of the Hydra service, particularly when attackers leverage the vulnerability to perform repeated resource exhaustion attacks against the evaluator infrastructure.
The vulnerability aligns with CWE-306, which addresses missing authentication, and represents a classic case of incomplete mediation where the system fails to properly validate all access attempts to protected resources. From an attack framework perspective, this issue maps to the attack technique of privilege escalation and resource exhaustion, potentially enabling adversaries to consume excessive computational resources through the API endpoints. The patch implemented in commit f7bda02 addresses this by enforcing proper authentication mechanisms for the affected endpoints, ensuring that only authorized parties can trigger evaluations through these interfaces. The recommended workaround of blocking these endpoints via reverse proxy serves as a temporary mitigation strategy that effectively prevents unauthorized access while maintaining system functionality for legitimate users who require the service through properly authenticated channels.
This vulnerability demonstrates the critical importance of implementing proper authentication mechanisms at all levels of API access control, particularly for services that handle resource-intensive operations. The combination of insufficient authentication with potentially resource-consuming operations creates a dangerous scenario that can lead to both unauthorized access and service disruption. Organizations utilizing Hydra or similar continuous integration services must ensure that all API endpoints are properly secured through multiple authentication layers, as relying solely on message signing without proper access control creates exploitable conditions that can be leveraged for both unauthorized access and denial of service attacks.