How To Bypass Web Application Firewall

The attempt to bypass a WAF or web application firewall is a critical aspect of the firewall penetration test. The WAF is meant to protect a web application through adding an extra security layer. In this sense, it will stand between the web server and user. It can also understand HTTP traffic much better compared to traditional firewalls. The WAF will therefore check for malicious web traffic and accordingly block it.

However, there are methods for bypassing the firewall too as mentioned below:

• Pre-processor exploitation: In this the WAF is made to skip input validation
• Impedance Mismatch: Here the WAF will interpret the inputs differently than the back-end.
• Rule-set bypassing: In this, payloads used fail to be detected by the WAF

The WAF can be configured in a way to skip input validations when the performance is very high. A huge volume of malicious requests may be sent hoping that the WAF will get overloaded and skip some requests. Again, many parameters can be sent having the same names. The WAF may see two individual parameters but fail to detect payload. Double URL encoding of a payload may lead to bypassing the WAF as the WAF has been configured for decoding characters only once.

So, various methods and techniques for bypassing the web application firewalls have been collected and classified. Depending upon these methods, practical approaches have been made. This approach will help to improve accuracy of the penetration test result. So, lists of bypassing WAF methods have been used by vendors for improving their WAFs. This means that while WAFs may make exploiting the vulnerabilities tough, they do not guarantee complete protection against security breaches.