The Net::HTTPS module in libwww-perl (LWP) before 6.00 as used in WWW::Mechanize LWP::UserAgent and other products when running in environments that do not set the If-SSL-Cert-Subject header does not enable full validation of SSL certificates by default which allows remote attackers to spoof servers via man-in-the-middle (MITM) attacks involving hostnames that are not properly validated. NOTE: it could be argued that this is a design limitation of the Net::HTTPS API and separate implementations should be independently assigned CVE identifiers for not working around this limitation. However because this API was modified within LWP a single CVE identifier has been assigned.