Mozilla Network Security Services (NSS) before 3.20.2, as used in Mozilla Firefox before 43.0.2 and Firefox ESR 38.x before 38.5.2, does not reject MD5 signatures in Server Key Exchange messages in TLS 1.2 Handshake Protocol traffic, which makes it easier for man-in-the-middle attackers to spoof servers by triggering a collision.

Affected: Ubuntu:14.04:LTS: nss

Karthikeyan Bhargavan and Gaetan Leurent discovered that NSS incorrectly allowed MD5 to be used for TLS 1.2 connections. If a remote attacker were able to perform a machine-in-the-middle attack, this flaw could be exploited to view sensitive information.