Red Hat Confidential Compute Attestation: improper signature check

A flaw was found in sequoia-openpgp. The library incorrectly infers key flags for older certificates when a key flags subpacket is missing, leading to a discrepancy in how key capabilities are viewed. This key flag confusion allows an attacker to bypass the back-signature check. Consequently, an attacker can illegitimately bind an arbitrary subkey to their own certificate and forge signatures, completely compromising cryptographic integrity.