PGP Corporate Desktop before 7.1, Personal Security before 7.0.3, Freeware before 7.0.3, and E-Business Server before 7.1 does not properly display when invalid userID's are used to sign a message, which could allow an attacker to make the user believe that the document has been signed by a trusted third party by adding a second, invalid user ID to a key which has already been signed by the third party, aka the "PGPsdk Key Validity Vulnerability."