mail/include.html in IceWarp Web Mail 5.5.1, as used by Merak Mail Server 8.3.0r and VisNetic Mail Server version 8.3.0 build 1, does not properly initialize the default_layout and layout_settings variables when an unrecognized HTTP_USER_AGENT string is provided, which allows remote attackers to access arbitrary files via a request with an unrecognized User Agent that also specifies the desired default_layout and layout_settings parameters.