How does Web Application Firewall Work?


The Web Application Firewall or WAF is responsible for filtering, monitoring and blocking HTTP web traffic going to and coming from web applications. It is distinct from a standard firewall because the WAF is designed to filter content in specific web apps while the regular firewalls will work like safety gates in between servers. Since it inspects HTTP traffic, it is able to ward off attacks which may arise because of security flaws in different web applications. Some of these commonly occurring attacks are the XSS attacks or cross-scripting attacks, DDoS attacks, SQL injection attacks etc.

How the WAF will work:

The WAF will scan the web traffic to detect suspicious and malicious activities. It then filters out the illegitimate traffic depending upon the rules you have specifically set down. It will address both POST and GET requests and then apply rule sets which will cover the various vulnerabilities and help you understand which traffic to block, which traffic to challenge and which traffic you can allow to pass. So, it will be able to block cross-scripting attacks and SQL injection attacks successfully. The WAFs are very common security tools being used by enterprises today for protecting their web apps from zero-day exploits. You can even deploy customized inspections which will allow the WAFs to detect and stop XSS attacks and SQL injection attacks, buffer overflows, session hijacking etc that other standard firewalls cannot successfully prevent.

The network-based WAF is typically hardware-based and it can lower the latency as it is locally installed and near the application. Majority of the network-based web application firewall vendors will allow rules replication across many devices and makes large scale c

onfigurations possible. But, the key drawback of such a system is the huge costs. On the other hand, the application based web application firewall will guarantee low costs of deployment and better customizability. The cloud-hosted WAFs are also very cost-effective for businesses which look for turnkey products. They are also easier to deploy and can be obtained on subscription basis.


The difference between a web application firewall (WAF), an intrusion prevention system (IPS) and a next-generation firewall (NGFW)

1. Web Application Firewall (WAF):

  • Functionality: A WAF is specifically designed to protect web applications from various types of cyber threats and attacks. It operates at the application layer of the OSI model, examining HTTP traffic between a web application and a user’s browser.
  • Focus: Its primary focus is on safeguarding web applications from common vulnerabilities like SQL injection, Cross-Site scripting (XSS), and other application-layer attacks.
  • Key Features: Signature-based detection, behavior analysis, and heuristics are commonly used techniques. It also provides tools for fine-tuning security policies to suit the specific needs of web applications.

2. Intrusion Prevention System (IPS):

  • Functionality: An IPS is a network security solution designed to monitor and analyze network traffic for suspicious activity or known attack patterns. It identifies and blocks potential threats based on predefined rulesets.
  • Focus: IPS is concerned with protecting the entire network infrastructure, including servers, workstations, and network devices, against various types of threats and attacks.
  • Key Features: It employs signature-based detection, anomaly-based detection, and protocol analysis to identify and prevent malicious activities.

3. Next-Generation Firewall (NGFW):

  • Functionality: NGFWs are advanced versions of traditional firewalls that incorporate additional features beyond packet filtering and stateful inspection. They combine firewall capabilities with intrusion prevention, application awareness, and other security features.
  • Focus: NGFWs are designed to provide comprehensive network security by understanding the context of traffic and making security decisions based on applications, users, and content.
  • Key Features: Deep packet inspection, application awareness, user identification, and integration with threat intelligence are some of the key features of NGFWs.

Key Differentiators:

1. Scope of Protection:

  • WAF focuses on safeguarding web applications.
  • IPS protects the entire network infrastructure.
  • NGFW provides network security with advanced features.

2. Layer of Operation:

  • WAF operates at the application layer.
  • IPS works at the network layer.
  • NGFW operates at both the network and application layers.

3. Primary Threats Addressed:

  • WAF primarily addresses web application vulnerabilities.
  • IPS targets a broader range of network-based threats.
  • NGFW provides a comprehensive defence against various types of threats.

4. Additional Capabilities:

  • WAF is specialised in web application protection.
  • IPS has a broader focus on network-wide threat prevention.
  • NGFW combines firewall capabilities with advanced security features.

WAF Deployment Modes:

1. Reverse Proxy Mode:

  • Description: In this mode, the WAF is positioned between the internet and the web server. It acts as a proxy, intercepting incoming traffic before it reaches the web server. The WAF then filters and inspects the traffic for potential threats or vulnerabilities before forwarding it to the web server.
  • Advantages: Provides an additional layer of security, allowing the WAF to inspect and filter traffic effectively. Offers flexibility in configuring security policies.

2.Transparent Mode:

  • Description: In transparent mode, the WAF is deployed in line with the network, but it does not change the IP address or network configuration of the web server. It passes traffic directly to the web server without altering the original packet headers.
  • Advantages: It preserves the original server configuration and does not require changes to network settings. Operates seamlessly within the existing network architecture.

3.Bridge Mode:

  • Description: Bridge mode involves placing the WAF between the firewall and the web server. It operates in such a way that it inspects traffic passing through it without modifying the packet headers. This mode allows the WAF to monitor and filter traffic without directly interacting with the IP addresses.
  • Advantages: It enables monitoring of traffic without requiring changes to the network configuration. Provides a non-intrusive method for inspecting traffic.

4.Inline Mode:

  • Description: In this mode, the WAF is placed directly in the path of traffic between the client and the web server. It actively intercepts and inspects traffic, allowing it to take immediate action to block or allow requests based on security policies.
  • Advantages: Provides real-time protection by actively intercepting and inspecting traffic. Allows for immediate response to potential threats.

5.Out-of-Path Mode:

  • Description: In out-of-path mode, the WAF monitors traffic by receiving a copy of the traffic stream rather than directly intercepting it. This allows the WAF to analyze traffic without being directly in the data path.
  • Advantages: minimizes potential impact on network performance. Provides an additional layer of security without directly intercepting traffic.

6.Load Balancer Integration:

  • Description: Some WAF solutions integrate seamlessly with load balancers. In this setup, the WAF works in conjunction with the load balancer to distribute traffic across multiple servers while also providing security checks and filtering.
  • Advantages: It ensures that traffic is evenly distributed across servers while also benefiting from WAF security features.

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