Summary The GHSA-6c99-87fr-6q7r fix wrapped WebAuthn authenticator deserialization in an "ObjectInputFilter" meant to allow only "AuthenticatorImpl", but it short-circuits to "ALLOWED" for any object at stream "depth > 1". Because the Java serialization filter is consulted for every class in the graph (and "depth == 1" only for the root's concrete class), the allowlist constrains only the root and leaves the entire nested graph unchecked. Impact An attacker can craft a stream rooted at "AuthenticatorImpl" with an arbitrary gadget chain nested inside. The gadget's "readObject"/"readResolve" executes during "readObject()" — before the cast and before any assertion verification — enabling remote code execution when a gadget is on the classpath. The deserialization sink is reached pre-authentication via an attacker-chosen "userHandle".