A flaw was found in the way the TLS protocol composes the Diffie-Hellman key exchange. A man-in-the-middle attacker could use this flaw to force the use of weak 512 bit export-grade keys during the key exchange, allowing them do decrypt all traffic. Please note that this update forces the TLS/SSL client implementation in NSS to reject DH key sizes below 768 bits, which prevents sessions to be downgraded to export-grade keys. Future updates may raise this limit to 1024 bits.