Description:
------------
Filter-0.9.4

stateOH1: /* state "octal or hex" */
	if (*p != '0') {
		goto stateI1;
	}
	p++;
	if (*p == 'x') {   <===HERE: not test 'X'
		if (allow_hex) {
			p++;
			goto stateH1;
		} else {
			goto stateE;
		}


stateH1: /* state "hex 1" */
	ctx_type = TYPE_HEX;
	if ((*p >= '0' && *p <= '9') || (*p >= 'a' && *p <= 'f')) { <<<===HERE: not test 'A' - 'F'
		ctx_value *= 16;
		if (*p >= '0' && *p <= '9') {
			ctx_value += ((*p) - '0');
		}
		if (*p >= 'a' && *p <= 'f') {
			ctx_value += 10 + ((*p) - 'a');
		}
		p++;
		goto stateH1;
	}


Reproduce code:
---------------
$source = INPUT_GET;
$name = $_GET['foo'];
$option = array('flags' => FILTER_FLAG_ALLOW_HEX);

$ret = input_get($source, $name, parent::FILTER_VALIDATE_INT, $options);

in $_GET['foo'] == 0XF; or 0xF or 0Xf;