The vulnerability stemmed from using session.clear() instead of session.flush() or cycle_key(). Clear() removes session data but preserves the session ID, enabling session fixation attacks. The patch replaced all clear() calls with user_logout (which calls flush()) and added session key cycling in auth_forms. The identified functions directly used the vulnerable session.clear() method prior to patching, as shown in the commit diffs. Each was modified in the security fix, confirming their role in the vulnerability.