A tool for testing if Web application firewalls (WAFs) are vulnerable to around 150 protocol-level evasion techniques was released at the Black Hat USA 2012 security conference on Wednesday.
The tool and the research that went into its creation are the work of Ivan Ristic, director of engineering at security vendor Qualys and the original author of the popular ModSecurity Web application firewall.
Web application firewalls are designed to protect Web applications from known attacks, such as SQL injection attacks, that are commonly used to compromise websites. They do this by intercepting requests sent by clients and enforcing strict rules about their formatting and payload.
However, there are various methods for sneaking malicious requests that violate these rules past WAFs by modifying certain parts of their headers or the paths of requested URLs. These are known as protocol-level evasion techniques, and WAFs are not properly equipped to deal with them at the moment because the techniques are not very well documented, Ristic said.
The researcher tested the evasion techniques he found primarily against ModSecurity, an open source Web application firewall, but it’s reasonable to assume that other WAFs are vulnerable to some of them as well.
In fact, Ristic said he shared a few of the techniques with others during the research stage and that they had tested them successfully against some commercial WAF products.
Erwin Huber Dohner, head of research and development at Switzerland-based WAF vendor Ergon Informatik, confirmed after seeing Ristic’s presentation that the evasion methods are a problem for the industry.
The question is will this public release of research kick-start a discussion as Mr. Ristic hopes?
- Vulnerabilities in open source WAF ModSecurity (net-security.org)
- Protocol-Level Evasion of Web Application Firewalls (community.qualys.com)
- Web Application Firewalls and the False Sense of Security They can Create (acunetix.com)