Summary
Rebuild versions through 4.4.7 and 4.5.0-beta5 contain an improper authentication flaw in the /user/login endpoint. A remote attacker may be able to bypass intended authentication checks, depending on deployment configuration and how the endpoint processes login requests.
Affected context
The vulnerability is associated with the Login Endpoint component of Rebuild and affects versions reported up to 4.4.7 and 4.5.0-beta5. Risk is present where the /user/login endpoint is remotely reachable and authentication decisions can be influenced by the flawed request-processing behavior.
Exploit preconditions
- Attack surface: The remotely accessible
/user/loginendpoint - Required access: Network access to the affected Rebuild service; valid credentials may not be required if authentication checks can be bypassed
- Trigger point: Processing of login requests by the authentication handler
- Why exploitation is possible: An authentication logic defect may cause the application to accept a request without correctly verifying the identity or authorization state
Why this happens
The underlying issue is an authentication validation failure that maps to CWE-287: Improper Authentication. The login flow does not reliably establish or verify the identity associated with a request before granting access, allowing input or state-handling behavior to circumvent intended authentication controls.
Potential impact
- An attacker may gain unauthorized access to protected application functionality
- User or administrative accounts could be impersonated
- Confidential application data may be exposed
- Unauthorized actions could be performed with the privileges assigned to the bypassed account
- The affected service could be used as a foothold for further activity
General mitigation guidance
Mitigation generally centers on making authentication decisions explicit, centralized, and fail-closed.
Common defensive patterns include:
- Enforcing complete server-side identity verification for every protected request
- Rejecting ambiguous, malformed, or incomplete authentication states by default
- Separating authentication from authorization and applying both consistently
- Avoiding client-controlled indicators as evidence of successful login
- Limiting privileged functionality according to least-privilege principles
- Protecting login endpoints with appropriate session, token, rate-limit, and monitoring controls
- Reviewing externally reachable authentication flows and reducing unnecessary exposure
How teams detect issues like this
Organizations can assess for this class of issue through:
- Static and semantic analysis of authentication branches, session establishment, and access-control decisions
- Code review checks for default-allow behavior, missing identity validation, and trust in client-controlled authentication state
- Integration tests covering unauthenticated, partially authenticated, expired-session, and privilege-boundary requests
- Policy enforcement requiring centralized authentication middleware for protected routes
- Monitoring for successful sessions or privileged actions that lack corresponding verified authentication events
- Automated security testing that evaluates authentication and authorization behavior across endpoint variations
