tssci security

Week of War on WAF's: Day 5 -- Final thoughts

Did we learn anything about web application firewall technology this week?

I hope so. However, my gut tells me there is an overriding feeling of ambiguity around this technology. People want WAFs, but they don't know why. Organizations everywhere think this is the best or only short-term answer to the web application security problem.

The PCI SSC, who has set June 30th, 2008 as the deadline for compliance with Requirement 6.6, also appears to be wishy-washy on the whole deal. I read the following two articles this morning about PCI-DSS Requirement 6.6 and the use of web application firewalls. While the titles of the articles may appear many are still leaning on or towards WAFs -- after reading the information and quotes, I think the titles might be misleading.

Web application security experts Mike Andrews and Robert Auger also have some interesting things to say. They seem to be very set on the idea that WAF (with proper blacklists) or VA+WAF (to manage the blacklists) are fair enough temporary solutions until organizations can implement secure coding.

Some interesting things can go wrong during the WAF implementation phase. I can identify the following problem areas that may have many organizations wondering why they went the WAF route:

  1. You think that a network engineer or network security expert could get up to speed quickly through training or lab-time. However, I think the average time to become a web application security expert is 3-4 years of specialization. Imagine how many developers could have been trained or worked on collaborative processes with IT security in that time period.
  2. Blacklist technology (especially VA+WAF) is going to help with false positives. However, what about general performance problems? If performance or availability issues occur, the first thing thrown out will be the WAF. What good is a device that is constantly removed from the architecture and then only put back in to meet compliance issues?
  3. There is a lot of technology out there to detect specific WAF products. It's been written about in books. Attack tools such as w3af utilize plugins such as detectWAF. Vulnerabilities exist in WAF products in the same way that they exist in all software. Adversaries are already using this information to their advantage. Using a WAF can indeed make you less secure. In order to provide a product that will protect modern web applications, we must first test the products ourselves. There is more complexity in the average WAF than in the average Intranet web application -- who is going to provide the countless hours of secure code review and manual pen-testing needed for these WAF products? Or are we going to use them blindly without considering the consequences?

What are some short-term alternatives?

  1. Multiple WAF solutions -- one solution that focuses on "outbound" web traffic, and another that is tuned to your specific application (e.g. language, framework, components in use, et al). If your web application uses well-formed, valid XHTML -- the outbound filtering requirement is already fulfilled. Refactoring your content to XHTML is a snap. Many books and tools exist to help in this process (Dreamweaver, xmllint, TagSoup, NekoHTML, and HTML Tidy just to name a few).
  2. A softer, lighter version of Agile/Test-first development practices with basic unit tests that correct input validation issues. This would be equivalent or better than WAF in practice. James Shore discusses how to implement this sort of idea in an article, Continuous Integration on a Dollar a Day.
  3. Even Aspect-oriented programming will show immediate value, as the cost proposition lowers when you already have the existing talent to implement AOP. If you have developers that know AspectJ -- input validation routines can be added with point-cuts almost overnight.

The problem with these three short-term solutions is that they involve talking to your development teams. Do they have a reason to avoid using valid XHTML? Maybe their waterfall mindset precludes them from being able to move to a situation where "building code" is more important than "programming" (although I would argue that it's a developer's job to write buildable code).

What I think is most sad about the state of WAF technology is that a single, cheap developer could easily replace all of the normal WAF functionality in the code using basic unit testing. A talented developer who knew AOP could do much more than a WAF, and still at a much lower overall cost. Some organizations that are implementing WAF are having the developers manage the solutions instead of network engineers or IT security. We're hoping that this situation will allow the developers to think up better ideas as well as learn where their applications are failing.

In fact, a non-developer: such as someone in marketing who uses Dreamweaver, could also do almost as much as a normal WAF by saving their content as valid XHTML. This would buy the organization basic application security functionality, which is what WAF also attempts to do.


We know that WAF's appear to be the easiest answer to the PCI-DSS Requirement 6.6. But what if there was an even more simple answer? Talk with your QSAC, QSA auditor, and an external third-party such as a web application vulnerability assessor, software risk expert, or strategy consultant about possible compensating controls, such as:

If you are going to choose a web application firewall, we suggest:

Rich Mogull also has some very new suggestions that he would like to see as a future for WAF in his blog post, The Future of Application and Database Security: Part 2, Browser to WAF/Gateway. It's also worth a read!

Posted by Dre on Friday, June 27, 2008 in Defense and Security.

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