The vulnerability centers on improper route access controls (CWE-288/CWE-863). In Drupal, route access is determined by access check services like TfaAccessCheck. The advisory explicitly states the module failed to prevent route overrides that bypass TFA, indicating the access control handler was deficient. The patched version's added route integrity checks and access enforcement further corroborate that the TfaAccessCheck::access method was the focal point of the authorization flaw. During exploitation, this function would appear in stack traces when attackers access overridden routes without proper TFA validation.