A design bug in X.509 certificate chain validation (RFC 3280) allows attackers to trigger (blind) HTTP requests for both external as well as internal IPs if a specially-crafted, S/MIME-signed email is opened in Microsoft Outlook. This issue, which has been originally reported in 2008, has been revisited and timing differences make it possible to identify open and closed ports on internal networks.
9365e6ebb217675995930a39307adaa0068c69e67328ec203f67fb4ba9ac8f00