Three ways WAFs Fail

Tuesday September 11 2018

Ah, the WAF. You might know it by its street name: the web application firewall. It’s a long standing technology that has been handed down from generation to generation from datacenter to cloud to serverless. Rarely effective, largely disliked.

In the land of web application security, there are a few not-so-well-kept secrets, arguably none bigger than this:

The WAF survided not by being excellent, but by being mandated.

The WAF is an antiquated technology that was created to help stem the rise of application security vulnerabilities, which had been overwhelming organizations with their frequency of discovery. Static and dynamic analysis tools dumped huge quantities of bugs onto development teams that had no possible way to fix so many code issues.

Meant as a stop gap measure to address this problem, the WAF made it possible to filter out rampant SQLi, command execution and XSS attacks that were threatening to consume all of the development and security team’s available resources. The idea behind the WAF was that the application bugs and security flaws would be triaged for now, and then eventually fixed in the code at the root of the problem.

At the time, a drop-in web application security filter seemed like a good idea. Sure, it sometimes led to blocking legitimate traffic, but such is life. It provided at least some level of protection at the application layer — a place where compliance regimes were desperate for solutions. Then PCI (Payment Card Industry) regulations got involved, and the whole landscape changed.

PCI requirement 6.6 states that you have to either have a WAF in place or do a thorough code review on every change to the application. Given the unappealing nature of the second option, most organizations read this as a mandate to get a WAF. In other words, people weren’t installing WAFs due to their security value — they just wanted to pass their mandatory PCI certification. It’s fair to say that PCI singlehandedly grew the WAF market from an interesting idea to the behemoth that it is today.

And the WAF continues to hang around, an outdated technology propped up by legalese rather than actual utility, providing a false sense of security without doing much to ensure it. If that isn’t enough for you to show your WAF the door, here are three more reasons why WAFs should be replaced.

Reason 1: The Minimum WAF Rules Approach is Broken

A common side effect of a WAF implementation is the blocking of legitimate traffic. In the application security business, we call these false positives. Don’t be fooled by this innocuous phrasing — what it means is that customers aren’t able to buy things they want, or upload their latest vacation photos or generally use the functionality of your applications. It’s the kind of experience that can quickly turn current customers into former customers.

To combat WAF false positives, most companies run the bare minimum number of rules to get by. This means that only the most obvious and most egregious attacks are caught, while everything else just sails right past the filter. Simple rules mean easy-to-bypass rules, leaving you with an ineffective WAF.

For reason 2 & 3, please see the original article which appeared in Signal Sciences Labs or come see us at Cyber Security Chicago .

Original article: https://labs.signalsciences.com/three-ways-wafs-fail .

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