鬼仔's Blog

文章作者：千寂孤城
信息来源：邪恶八进制信息安全团队

一、方法

1、先进后台。利用CheckUserLogined漏洞直接加个后台管理员。关于这个CheckUserLogined漏洞我在《Blog的噩梦》（http://www.eviloctal.com/forum/htm_data/10/0508/13721.html ）中有详细的说明，大概就是说可以通过Cookies欺骗搞SQL注入。
2、在后台的“网站信息配置”处有个“普通会员上传文件类型”，给它加一个aaaspspsp类型。
3、用个普通帐号登陆，来到上传文件的页面http://blog.***.com/upload.asp ，看到了吗？可上传文件多了个“aaspsp”类型。好，把你的马x.asp改名为x.aaspsp，然后传上去。
4、到你自己的blog后台去看一看，是不是成功上传了x.asp了？：）

二、原理

本来刚开始我是直接在后台的“普通会员上传文件类型”里加了个“|asp”，结果发现上传失败。于是去Down个oBlog 2.52下来。读了读upload.asp的代码，大家一起看看：
’初始化上传限制数据
Sub InitUpload()
……
Select Case cint(DecodeCookie(Request.Cookies(cookiesname)("userlevel")))
Case 7
if rs("upfile_user")="true" then
themax=round(user_maxsize-theuped/1024)
sAllowExt = rs("upfile_user_type") ’注意这里，得到我们在后台设置的可上传文件的类型，放入sAllowExt变量中
if themax>rs("upfile_user_size") then
nAllowSize = rs("upfile_user_size")
else
nAllowSize = themax
end if
else
sAllowExt = "暂无上传权限"
nAllowSize = 0
end if
……
End Select
sAllowExt = filtfilename(sAllowExt) ’这里是对sAllowExt进行检查
……
End Sub

以上代码是说如果是普通用户，那么就给字符串sAllowExt赋值为我们在后台设定的那个“普通会员上传文件类型”：jpg|png|bmp|rar|zip|asp。但是请注意，sAllowExt然后还必须经过filtfilename()的检查。再接着看：
’保存操作
Sub DoSave()
Set oFile = oUpload.File("uploadfile")
sFileExt = UCase(oFile.FileExt)
osize = oFile.Filesize
Call CheckValidExt(sFileExt) ’检查文件扩展名是不是sAllowExt里有的
sFileExt=filtfilename(sFileExt) ’哎，filtfilename又来了
……
oFile.SaveToFile Server.Mappath(sUploadDir & "/"& sFileName)
……
End Sub

以上代码就是说文件扩展名必须是sAllowExt里有的然后才能上传。上传后保存到目标计算机上时扩展名还要被filtfilename过滤一次。那么那个filtfilename到底是什么东西呢？我们看看：
Function filtfilename(filename)
If IsEmpty(filename) Then Exit Function
filename = Lcase(filename)
filename = Replace(filename,Chr(0),"")
filename = Replace(filename,".","")
filename = Replace(filename,"asp","")
filename = Replace(filename,"asa","")
filename = Replace(filename,"aspx","")
filename = Replace(filename,"cer","")
filename = Replace(filename,"cdx","")
filename = Replace(filename,"htr","")
filename = Replace(filename,"asax","")
filename = Replace(filename,"ascx","")
filename = Replace(filename,"ashx","")
filename = Replace(filename,"asmx","")
filename = Replace(filename,"axd","")
filename = Replace(filename,"vsdiso","")
filename = Replace(filename,"rem","")
filename = Replace(filename,"soap","")
filename = Replace(filename,"config","")
filename = Replace(filename,"cs","")
filename = Replace(filename,"csproj","")
filename = Replace(filename,"vb","")
filename = Replace(filename,"vbproj","")
filename = Replace(filename,"webinfo","")
filename = Replace(filename,"licx","")
filename = Replace(filename,"resx","")
filename = Replace(filename,"resou","")
filename = Replace(filename,"jsp","")
filename = Replace(filename,"php","")
filename = Replace(filename,"cgi","")
filtfilename=filename
End Function

是过滤函数，害我们不成功的就是这个东西。
嘿嘿，看完了，基本上也明白了。理一下思路，简单一点说就是后台设定的上传类型要经过Replace(filename,"asp","")检查两次（晕……麻不麻烦）。仔细想一想，这里是有漏洞的！我们可以用“aaaspspsp”来绕过它！
于是我们把“普通会员上传文件类型”那里加上“|aaaspspsp”。然后用个普通用户登陆，来到上传处。可上传文件就多了个“aaspsp”类型。这是因为“aaaspspsp”经过第一次过滤，把中间的那个“asp”过滤掉了，变成了“aaspsp”。
然后我们把马儿的名字改成x.aaspsp传上去，在服务器在保存马儿时把它的扩展名“aaspsp”第二次过滤后就还原成了“asp”，就成功搞到webshell了。

三、漏洞修补

CheckUserLogined漏洞修补方法：在inc/function.asp的CheckUserLogined()函数中加上password=ReplaceBadChar(trim(password))。

upload.asp漏洞修补方法：把filtfilename函数改成循环的：
Function filtfilename(filename)
If IsEmpty(filename) Then Exit Function
filename = Lcase(filename)
do ’开始循环
A_len=len(filename) ’得到字符串长度
filename = Replace(filename,Chr(0),"")
filename = Replace(filename,".","")
filename = Replace(filename,"asp","")
filename = Replace(filename,"asa","")
filename = Replace(filename,"aspx","")
filename = Replace(filename,"cer","")
filename = Replace(filename,"cdx","")
filename = Replace(filename,"htr","")
filename = Replace(filename,"asax","")
filename = Replace(filename,"ascx","")
filename = Replace(filename,"ashx","")
filename = Replace(filename,"asmx","")
filename = Replace(filename,"axd","")
filename = Replace(filename,"vsdiso","")
filename = Replace(filename,"rem","")
filename = Replace(filename,"soap","")
filename = Replace(filename,"config","")
filename = Replace(filename,"cs","")
filename = Replace(filename,"csproj","")
filename = Replace(filename,"vb","")
filename = Replace(filename,"vbproj","")
filename = Replace(filename,"webinfo","")
filename = Replace(filename,"licx","")
filename = Replace(filename,"resx","")
filename = Replace(filename,"resou","")
filename = Replace(filename,"jsp","")
filename = Replace(filename,"php","")
filename = Replace(filename,"cgi","")
loop until A_len=len(filename) ’如果过滤前的长度等于过滤后的长度说明已经过滤得干干净净了，退出循环。
filtfilename=filename
End Function