Attack Chain

1. Attacker identifies target application: An attacker identifies a web application that is developed using the DotVVM framework.
2. Vulnerability discovery: The attacker becomes aware of the AuthorizeActionFilter authorization bypass vulnerability (GHSA-c8qj-jx8j-fg2w) in DotVVM, understanding its nature as a complete bypass.
3. Endpoint identification: The attacker probes or researches the target application to identify specific web application endpoints or functionalities that are intended to be protected by the vulnerable AuthorizeActionFilter (e.g., /admin, /dashboard, /api/users).
4. Craft unauthorized request: The attacker crafts a standard HTTP GET or POST request to one of these identified protected endpoints, intentionally omitting or providing insufficient authentication or authorization tokens.
5. Application processes request: The vulnerable DotVVM application receives and processes the crafted HTTP request, routing it to the appropriate controller action.
6. Filter execution (no check): The AuthorizeActionFilter component, despite being invoked for the protected endpoint, executes without performing any authorization validation due to its internal flaw, effectively doing nothing.
7. Unauthorized access granted: The DotVVM application, mistakenly assuming authorization has occurred, proceeds to execute the action and grants the attacker full access to the intended protected resource or functionality.
8. Impact achieved: The attacker successfully bypasses security controls, leading to unauthorized data exposure, privilege escalation, or the ability to perform restricted actions within the compromised application.

Impact

All applications utilizing the AuthorizeActionFilter class within the specified vulnerable DotVVM versions are at critical risk. The complete failure of the filter to perform any authorization checks means that any resource or functionality intended to be protected by it is openly accessible to unauthorized individuals. This directly leads to unauthorized access to sensitive data, compromise of administrative functions, or complete takeover of application features that were meant to be restricted. The number of potentially affected applications is widespread among DotVVM users who relied on this specific authorization mechanism for security.

Recommendation

• Patch immediately: Upgrade all affected DotVVM installations to a patched version (DotVVM 4.3.15, 4.2.11, or 5.0.0-preview09) to remediate the GHSA-c8qj-jx8j-fg2w vulnerability.
• Implement workaround: For immediate protection if patching is not feasible, replace all instances of AuthorizeActionFilter with AuthorizeAttribute in your DotVVM application code.
• Monitor webserver logs: Deploy the Sigma rules "Detect Successful Access to Common Sensitive Web GET Paths" and "Detect Successful Access to Common Sensitive Web POST Paths" to monitor for HTTP 200 responses to known administrative or sensitive URIs, as this can indicate potential unauthorized access.
• Application-level logging: Implement robust application-level logging for all sensitive actions and authorization events to identify successful access to resources that should require specific permissions.