轻松获得oblog2.52的WebShell

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oBlog2.52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
SubInitUpload()
……
SelectCasecint(DecodeCookie(Request.Cookies(cookiesname)("userlevel")))

Case7
ifrs("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

ifthemax>rs("upfile_user_size")then
nAllowSize=rs("upfile_user_size")
else
nAllowSize=themax
endif
else
sAllowExt="暂无上传权限"
nAllowSize=0
endif
……
EndSelect
sAllowExt=filtfilename(sAllowExt)’这里是对sAllowExt进行检查

……
EndSub

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
SubDoSave()
SetoFile=oUpload.File("uploadfile")
sFileExt=UCase(oFile.FileExt)
osize=oFile.Filesize
CallCheckValidExt(sFileExt)’检查文件扩展名是不是sAllowExt里有的

sFileExt=filtfilename(sFileExt)’哎，filtfilename又来了
……
oFile.SaveToFileServer.Mappath(sUploadDir&"/"&sFileName)

……
EndSub

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：

Functionfiltfilename(filename)
IfIsEmpty(filename)ThenExitFunction
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
EndFunction

是过滤函数，害我们不成功的就是这个东西。