Martin von Gagern discovered that GNUTLS, an implementation of the TLS/SSL protocol, handles verification of X.509 certificate chains incorrectly if a self-signed certificate is configured as a trusted certificate. This could cause clients to accept forged server certificates as genuine. (CVE-2008-4989) In addition, this update tightens the checks for X.509v1 certificates which causes GNUTLS to reject certain certificate chains it accepted before. (In certificate chain processing, GNUTLS does not recognize X.509v1 certificates as valid unless explicitly requested by the application.)