What Is A Web Application Firewall (WAF)?

A Web Application Firewall (WAF) is a security firewall technology that protects web applications from HTTP and web application-based security flaws.  WAF systems have specific knowledge of HTTP and web application vulnerabilities and filters or blocks these attacks without ever exposing the web servers or applications.

A WAF is deployed between application servers and network edge routers and firewalls.  The web application firewall functions as a flexible barrier that filters all application access, inspecting both in-bound and out-bound traffic. It is specifically designed to mitigate attacks without blocking legitimate users and without slowing down application performance.

A web application firewall differs from a traditional network firewall in its ability to inspect data at the application level—for example, by validating form field input or protecting application cookies. A network firewall and a web application firewall are generally deployed together and provide complementary levels of security.

Threat Vectors

Applications can be vulnerable to many threats that are not detected by regular network firewalls. The impact of these attacks can be quite severe. The Open Web Application Security Project (OWASP) has compiled a list of the top 10 risks that still threaten many web application deployments. The top 10 of 2010 is virtually identical to the new 2013 version; the most common attacks have not changed dramatically over the years. Here are some examples:

  • InjectionSQL Injection Attacks use a Web form or other mechanism to send SQL commands or commands containing SQL special characters. By sending these SQL commands, the attacker can trigger the backend SQL database to execute the injected commands and allow unauthorized users to obtain sensitive information from the database.  
  • Cross-site scripting (XSS)XSS attacks exploit a Web server that does not validate data coming from another site. XSS can enable the attacker to obtain sensitive information, or to compromise a Web server.  
  • Sensitive data exposure: If Web applications do not protect sensitive data such as credit card numbers or Social Security Numbers (SSN), attackers are able to conduct identity theft, credit card fraud, or other crimes.  
  • Cross-site request forgery (CSRF)CSRF attacks force a user to send an HTTP request, including the victim's session cookie, to a vulnerable web application. To the vulnerable web application, this appears to be a legitimate request coming from the victim.

Attack Mitigation Examples

The WAF module offers granular control of Web application data flows. The WAF has various ways of dealing with threat vectors that can be launched at web applications. Here are two use cases:

  • The WAF can prevent buffer overflow attacks by setting accepted maximum thresholds for aspects of HTTP requests and blocking requests that exceed the configured limits. 
  • The WAF can strip HTTP response headers to “cloak” server information that can equip a hacker to target an attack on your Web servers. For example, the WAF can cloak an HTTP response header to hide the operating system that is running.

How Can A10 Help?

The A10 Thunder Application Delivery Controllers (ADCs) include a full featured WAF that blocks web attacks before they can reach vulnerable applications. Deployed as a proxy in front of web servers, Thunder ADC inspects web requests and responses and can block, sanitize, or log malicious activity.

The WAF enables a full defense stack with other A10 security mechanisms in order to protect web applications, ensure against code vulnerabilities and prevent data leakage; this aids in regulatory security compliance, such as Payment Card Industry Data Security Standard (PCI DSS) requirements.

A10's WAF feature is designed to recognize many of today's threats, with flexibility to customize checks for emerging threats. The WAF is tightly integrated with other A10 security features within the Advanced Core Operating System (ACOS). Instead of integrating 3rd party WAF code, as many other vendors do, A10 has developed the WAF specifically for ACOS. This approach results in a highly scalable and high performance security solution which is simple to configure.