Ory · Ory Fosite · CVE-2020-15234
**Name of the Vulnerable Software and Affected Versions**
ORY Fosite versions prior to 0.34.1
**Description**
The issue arises from the comparison of the OAuth 2.0 Client's registered redirect URLs and the redirect URL provided at the OAuth2 Authorization Endpoint using strings.ToLower instead of a simple string match. This allows an attacker to register a client with an allowed redirect URL, such as https://example.com/callback, and then perform an OAuth2 flow requesting a redirect URL like https://example.com/CALLBACK. As a result, the browser is redirected to https://example.com/CALLBACK with a potentially successful OAuth2 response, depending on the state of the overall OAuth2 flow.
**Recommendations**
For versions prior to 0.34.1, update to ORY Fosite version 0.34.1 to resolve the issue. As a temporary workaround, consider disabling the OAuth2 flow for clients with registered redirect URLs that may be exploited until a patch is applied. Restrict access to the OAuth2 Authorization Endpoint to minimize the risk of exploitation. Avoid using case-insensitive comparisons for redirect URLs in the affected OAuth2 flow until the issue is resolved.