cgi/b on the BT Home Hub router allows remote attackers to bypass authentication, and read or modify administrative settings or make arbitrary VoIP telephone calls, by placing a character at the end of the PATH_INFO, as demonstrated by (1) %5C (encoded backslash), (2) '%' (percent), and (3) '~' (tilde).  NOTE: the '/' (slash) vector is already covered by CVE-2007-5383.