Question

I’m on a short-term contracting gig, trying to patch some vulnerabilities in their legacy code. The application I’m working on is a combination of Classic ASP (VBScript) and .Net 2.0 (C#). One of the tools they have purchased is Fortify 360.

Here is a current classic ASP page in the application:

<%@ Language=VBScript %>
<%
Dim var

var = Request.QueryString("var")
' do stuff
Response.Redirect "nextpage.asp?var=" & var
%>

I know, I know, short and very dangerous.

So we wrote some (en/de)coders and validation/verification routines:

<%@ Language=VBScript %>
<%
Dim var

var = Decode(Request.QueryString("var"))
' do stuff
if isValid(var) then 
    Response.Redirect "nextpage.asp?var=" & Encode(var)
else
   'throw error page
end if
%> 

And still Fortify flags this as vulnerable to Header Manipulation. How or what exactly is Fortify looking for?

The reason I suspect that Fortify is looking for specific keywords is that on the .Net side of things, I can include the Microsoft AntiXss assembly and call functions such as GetSafeHtmlFragment and UrlEncode and Fortify is happy.

Any advice?

Answer 1

Jarret R is right; you will need to use the rules builder to create a Dataflow Cleanse rule; specify the function name as lowercase and the language as “vb”.

Your rule should look something like this:

        <DataflowCleanseRule formatVersion="3.10" language="vb">
            <RuleID>12345-67890-BABE-CAFE</RuleID>
            <TaintFlags>-XSS,+VALIDATED_CROSS_SITE_SCRIPTING</TaintFlags>
            <FunctionIdentifier>
                <NamespaceName>
                    <Pattern/>
                </NamespaceName>
                <ClassName>
                    <Pattern/>
                </ClassName>
                <FunctionName>
                    <Pattern CaseInsensitive="true">(?i)decode</Pattern>
                </FunctionName>
                <ApplyTo implements="true" overrides="true" extends="true"/>
            </FunctionIdentifier>
            <OutArguments>return</OutArguments>
        </DataflowCleanseRule>