WebKit, as used in Apple Safari before 5.0.4 and iOS before 4.3, does not properly handle redirects in conjunction with HTTP Basic Authentication, which might allow remote web servers to capture credentials by logging the Authorization HTTP header.
http://www.securitytracker.com/id?1025182
http://support.apple.com/kb/HT4566
http://support.apple.com/kb/HT4564
http://lists.apple.com/archives/security-announce/2011//Mar/msg00004.html
http://lists.apple.com/archives/security-announce/2011//Mar/msg00003.html