Authorizer Unvalidated Redirect Vulnerability Allows OAuth2 Token Theft

A critical unvalidated redirect vulnerability (CVE-2026-54072) in the Authorizer platform allows attackers to steal sensitive OAuth2 tokens. This flaw affects Authorizer versions prior to 0.0.0-20260409051328-bd3f5baf6d3d. An unauthenticated attacker can exploit this by first querying the publicly accessible /graphql endpoint to retrieve a valid client_id. They then craft a malicious URL targeting the /authorize endpoint, embedding an arbitrary, attacker-controlled redirect_uri. If a logged-in victim clicks this link, the Authorizer application performs a 302 redirect to the attacker's specified URL, appending the victim's access_token, id_token, and refresh_token as query parameters. This enables the attacker to intercept these tokens and impersonate the victim for the tokens' entire lifetime, bypassing authentication mechanisms. A partial fix was applied in v2.0.1 for other handlers, but the /authorize endpoint was overlooked.

Attack Chain

1. Attacker queries the public /graphql endpoint (e.g., http://TARGET/graphql) to obtain the client_id parameter, which is required for authorization requests.
2. The attacker crafts a malicious URL, including the obtained client_id and a controlled redirect_uri (e.g., https://attacker.com/steal), pointing to the vulnerable Authorizer /authorize endpoint.
3. The malicious URL (e.g., http://TARGET/authorize?response_type=token&client_id=...&redirect_uri=https://attacker.com/steal) is delivered to a logged-in victim, typically via social engineering.
4. When the victim clicks the malicious link, their browser sends an HTTP GET request to the Authorizer /authorize endpoint.
5. The Authorizer server, lacking proper validation for the redirect_uri parameter against AllowedOrigins, processes the request.
6. The server issues a 302 HTTP redirect response, appending the victim's access_token, id_token, and refresh_token as query parameters to the attacker-controlled redirect_uri.
7. The victim's browser automatically follows the redirect, sending the sensitive tokens to the attacker's server.
8. The attacker receives and logs the tokens, gaining unauthorized access to the victim's account and the ability to impersonate them.

Impact

Successful exploitation of CVE-2026-54072 results in the complete compromise of a victim's OAuth2 tokens, including access_token, id_token, and refresh_token. An attacker can then use these stolen tokens to impersonate the victim and access resources or perform actions on their behalf for the full duration of the token's validity, without any further user interaction beyond the initial click. While the specific number of victims or targeted sectors is not disclosed, any organization using affected versions of Authorizer is at risk of account takeover and unauthorized data access.

Recommendation

• Patch CVE-2026-54072 immediately by updating Authorizer to a patched version (newer than 0.0.0-20260409051328-bd3f5baf6d3d).
• Deploy the Sigma rule "Detects CVE-2026-54072 Exploitation - Malicious redirect_uri in Authorizer /authorize Endpoint" to your SIEM to detect attempts at exploiting this vulnerability.
• Block attacker.com at your network perimeter, including DNS resolvers and web proxies.