PGP 5.5.x through 6.5.3 does not properly check if an Additional Decryption Key (ADK) is stored in the signed portion of a public certifica…

PGP 5.5.x through 6.5.3 does not properly check if an Additional Decryption Key (ADK) is stored in the signed portion of a public certificate, which allows an attacker who can modify a victim's public certificate to decrypt any data that has been encrypted with the modified certificate.