CVE-2026-71885 MLS X.509 credential not bound to the LeafNode signature key

In Bouncy Castle for Java before 1.86, the Messaging Layer Security MLS, RFC 9420 implementation did not bind an X.509 credential to a LeafNode's signaturekey. LeafNode.verify checked a leaf's signature against the signaturekey carried in the leaf itself, while the credential's X.509 certificate...