Bugzilla 3.5.x and 3.6.x before 3.6.9, 3.7.x and 4.0.x before 4.0.6, and 4.1.x and 4.2.x before 4.2.1, when the inbound_proxies option is enabled, does not properly validate the X-Forwarded-For HTTP header, which allows remote attackers to bypass the lockout policy via a series of authentication requests with (1) different IP address strings in this header or (2) a long string in this header.