Interpretation conflict in ModSecurity (mod_security) 2.1.0 and earlier allows remote attackers to bypass request rules via application/x-www-form-urlencoded POST data that contains an ASCIIZ (0x00) byte, which mod_security treats as a terminator even though it is still processed as normal data by some HTTP parsers including PHP 5.2.0, and possibly parsers in Perl, and Python.