Web Application Firewalls: Key Configurations for Enhanced Security

In today's digital era, web applications are constantly under threat from various types of cyberattacks. A Web Application Firewall (WAF) plays a critical role in protecting these applications by filtering and monitoring HTTP traffic between a web application and the Internet. This blog post aims to demonstrate various ways to harden your WAF to enhance web application security.

Identifying OWASP Top 10 Threats with Specific Rules

The OWASP Top 10 is a security framework representing the most common and critical security risks to web applications. A well-configured WAF should have rules that utilize both signature-based and anomaly-based detection logic. An example of a signature rule could be detecting unusual protocols (e.g., `file://`). You can also look for elements such as `burpcollaborator.net` in an HTTP request to determine if an attacker is attempting to make a request call home. An example of anomaly detection is leveraging features from WAF providers that detect bot traffic. This anomaly detection baselines activity against your domain to determine which traffic looks automated versus what appears to be human traffic, aiming to successfully identify malicious bots. Such proactive measures are crucial for the early detection and prevention of these common yet dangerous threats.

Geo-Fencing in Highly Regulated Industries

Geo-fencing is another significant feature for WAF configurations, especially in highly regulated industries like finance and healthcare. This feature enables the restriction of web traffic from specific geographic locations. For instance, if a U.S.-based financial service observes repeated malicious attempts from a particular country, geo-fencing can block or scrutinize traffic from that region more stringently. This not only enhances security but also helps in complying with regional regulatory requirements.

Global Rate Limiting to Mitigate DDoS Attacks and Credential Stuffing

Distributed Denial of Service (DDoS) and credential stuffing attacks can overwhelm web applications with traffic. Implementing global rate-limiting rules in the WAF can mitigate these attacks. These rules restrict the number of requests a user can make in a given period, preventing servers from being overloaded by too many requests. This not only helps in maintaining the availability of the web application but also in safeguarding against such brute-force attack tactics.

Blocking Known Malicious User Agent Strings

Although it may not be the most accurate method since they can be spoofed, building a dictionary of known malicious user agent strings can help thwart inexperienced attackers. User agents like `nmap` or `nuclei` are often used for legitimate purposes but can also be utilized for reconnaissance by attackers. Configuring the WAF to block or flag requests from these user agents can prevent potential security breaches.

Integrating Threat Intelligence Feeds

To stay ahead of emerging threats, WAFs should consume threat intelligence feeds. These feeds provide real-time information about new vulnerabilities, attack patterns, and bad IP addresses. By integrating these feeds, the WAF can dynamically update its rules to protect against the latest threats, offering a more robust defense mechanism. It's important to distinguish between good and bad threat intelligence, as threat intelligence may or may not be applicable. For example, a list created without any verification may have a large false positive rate, whereas threat intelligence feeds built from analyzing customers in a specific vertical (e.g., banks using FS-ISAC for a threat intelligence feed since this is made up of known threat intelligence from banks globally) can accurately block malicious traffic.

Detecting Malicious Techniques

Finally, WAFs should be configured to identify malicious techniques used by attackers, such as base64 encoding and double encoding payloads. These techniques are often used to obfuscate malicious code, making it crucial for WAFs to decode and analyze such payloads to identify potential threats.

Conclusion

A Web Application Firewall is a formidable line of defense against a myriad of cyber threats. It should not be your only defensive measure, but can be successful when paired with practices such as code scanning and comprehensive audit logging of requests. By configuring the WAF to detect OWASP Top 10 risks, implementing geo-fencing, setting global rate limits, blocking malicious user agents, integrating threat intelligence feeds, and identifying obfuscation techniques, organizations can significantly enhance the security of their web applications. As cyber threats evolve, so should the strategies to combat them, and a well-configured WAF is key in this ongoing battle.