In Bouncy Castle for Java versions prior to 1.86, the OpenPGP certificate API's methods getCertificationBy() and getDelegationBy() accepted third-party signatures from any component key of the issuing certificate without verifying that the component held the RFC 9580 section 5.2.3.29 CERTIFY_OTHER key flag at the time of signature creation. This allowed subkeys bound only for signing or encryption (which can also sign) to issue valid User ID certifications or direct-key trust delegations, which the API treated as valid and attributed to the issuing certificate. The vulnerability does not forge the primary key's signature or expose private keys but allows an attacker-controlled subkey to gain certification authority improperly. The fix requires that third-party certifications or delegations be accepted only if the signing component is the primary key or a subkey with the CERTIFY_OTHER flag at signature creation.

The vulnerability enables an attacker controlling a restricted subkey to issue valid certifications or trust delegations that the API accepts as legitimate, effectively elevating the subkey's authority to that of the primary key's identity-issuing capability. This undermines the containment intended by key flag separation, potentially allowing unauthorized trust assertions. However, it does not compromise the primary key's private key or forge its signature. There are no known exploits in the wild.

No official patch or remediation details are provided in the input data. Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is applied, applications should be cautious in treating getCertificationBy(...).isValid() or getDelegationBy(...) results as definitive trust or identity decisions without additional validation of key flags.