The File Systems component in Apple Mac OS X before 10.7.2 does not properly track the specific X.509 certificate that a user manually accepted for an initial https WebDAV connection, which allows man-in-the-middle attackers to hijack WebDAV communication by presenting an arbitrary certificate for a subsequent connection.
http://www.securityfocus.com/bid/50085
http://support.apple.com/kb/HT5002
http://lists.apple.com/archives/Security-announce/2011//Oct/msg00003.html