Attack Chain

1. An attacker crafts a malicious website (attacker.com) containing JavaScript code that exploits the CORS misconfiguration.
2. The attacker lures an Open WebUI administrator to visit the malicious website.
3. The JavaScript on the attacker’s website bypasses CORS restrictions due to the allow_origins=["*"] configuration.
4. The malicious script sends an authenticated POST request to the /api/v1/functions/create endpoint, creating a malicious filter. This step requires the user to have an active Open WebUI session.
5. The attacker’s script then sends another POST request to /api/v1/functions/id/{filter_id}/toggle to activate the newly created filter, executing arbitrary code.
6. The code injected by the filter executes a command (e.g., whoami) and writes the output to a file (/tmp/whoami.txt) on the Open WebUI server.
7. Because Open WebUI reuses session cookies after logout, the attacker can potentially regain access even if the admin has logged out, provided the browser hasn’t been closed.
8. The attacker achieves remote code execution on the Open WebUI server, with the potential to fully compromise the Docker container due to the default root user context.

Impact

Successful exploitation of this vulnerability allows an attacker to execute arbitrary code on the Open WebUI server. Given the default configuration where Open WebUI runs as root within a Docker container, this can lead to a complete compromise of the container and potentially the host system. The vulnerability affects any Open WebUI instance with an administrator who visits the malicious website, making it a widespread risk. The lack of session invalidation post-logout increases the window of opportunity for attackers, even if the admin user is no longer actively using the application.

Recommendation

• Modify the Open WebUI CORS configuration to remove the permissive allow_origins=["*"] and implement a more restrictive policy. Allow dynamic setup of allowed origins via the administration panel or a configuration file, as described in the remediation guidance for GHSL-2024-174.
• Implement proper session invalidation upon logout. Ensure new cookies are generated for every session, and invalidate/remove previous session cookies from the browser’s storage upon logout, as described in the remediation guidance for GHSL-2024-175.
• Deploy the Sigma rule “Detect Open WebUI Function Creation via API” to identify potential exploitation attempts targeting the /api/v1/functions/create endpoint.