A flaw was found in Keycloaks SAML brokering functionality. When Keycloak is configured as a client in a Security Assertion Markup Language (SAML) setup, it fails to validate the NotOnOrAfter timestamp within the SubjectConfirmationData. This allows an attacker to delay the expiration of SAML responses, potentially extending the time a response is considered valid and leading to unexpected session durations or resource consumption.
Weakness
The product accepts XML from an untrusted source but does not validate the XML against the proper schema.
Potential Mitigations
- Always validate XML input against a known XML Schema or DTD.
- It is not possible for an XML parser to validate all aspects of a document’s content because a parser cannot understand the complete semantics of the data. However, a parser can do a complete and thorough job of checking the document’s structure and therefore guarantee to the code that processes the document that the content is well-formed.