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ORY Fosite is a security first OAuth2 & OpenID Connect framework for Go. In Fosite before version 0.34.1, the OAuth 2.0 Client's registered redirect URLs and the redirect URL provided at the OAuth2 Authorization Endpoint where compared using strings.ToLower while they should have been compared with a simple string match. This allows an attacker to register a client with allowed redirect URL https://example.com/callback. Then perform an OAuth2 flow and requesting redirect URL https://example.com/CALLBACK. Instead of an error (invalid redirect URL), the browser is redirected to https://example.com/CALLBACK with a potentially successful OAuth2 response, depending on the state of the overall OAuth2 flow (the user might still deny the request for example). This vulnerability has been patched in ORY Fosite v0.34.1.
Cite this page
CVE-2020-15234. CVEDatabase.com. Retrieved 1 May 2026. https://cvedatabase.com/cve/CVE-2020-15234
Use CWE-20, Ory vendor hub and Fosite product page to widen CVE-2020-15234 into its surrounding weakness, vendor, and product context.
Compare it with CVE-2020-15222, CVE-2020-15223 and CVE-2020-15233 for nearby disclosures in the same product family.