How can I avoid a CRLF injection for the below code? The response.appendheader is prone to CRLF injection attack.

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<%   
    Response.Clear()
    Response.ContentType = "application/force-download"    
    Response.AppendHeader("Content-Disposition", "attachment; filename=""" & Server.UrlEncode(Request.QueryString("filename"))& """")                      
    Response.Buffer = True
    Response.Flush()
    Response.WriteFile(Request.QueryString("path"))
    Response.End()
%>

What I have tried:

I have tried to do a Server.URLencode

Posted 9-Apr-18 3:54am

Member 13734676

Updated 9-Apr-18 4:00am

v2

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Dave Kreskowiak · Answer 1 · 2018-04-09T04:02:00

Simple. Don't EVER directly use user input in your response.

You're using Request.QueryString("filename") and Request.QueryString("path") directly in the response without ever processing the filename and path strings to make sure they

1) Have values at all (not null or empty)
2) Does not have invalid characters in what is expected to be a filename or path, like CR and LF.

This is trivial stuff. ALWAYS, ALWAYS, ALWAYS validate user input before you try to use it.