Directory Traversal was discovered in University of Cambridge mod_ucam_webauth before 2.0.2. The key identification field ("kid") of the IdP's HTTP response message ("WLS-Response") can be manipulated by an attacker. The "kid" field is not signed like the rest of the message, and manipulation is therefore trivial. The "kid" field should only ever represent an integer. However, it is possible to provide any string value. An attacker could use this to their advantage to force the application agent to load the RSA public key required for message integrity checking from an unintended location.