How WAF Works To Enhance Your App's Security

APIs are the backbone of many applications. But granting unrestricted access to them is like leaving your house's front door wide open.

You wouldn't let just anyone in, would you? Sure, some guests are welcome – the ones bringing delicious treats (those are always welcome). But others? Not so much.

Similarly, certain internal services need access to your APIs, but malicious traffic can exploit vulnerabilities and wreak havoc. This is where web application firewall (WAF) solutions step in.

But simply deploying a WAF isn't enough. Understanding how it works empowers you to fine-tune its configuration, maximizing your application's security posture.

WAF architecture

The architecture of a WAF typically involves several key elements and configurations that collectively enhance the security posture of web applications.

• Reverse proxy receives requests from clients, inspects them for potential threats, and then forwards the safe requests to the web server. Malicious traffic is blocked before it even reaches the application server.
• Rule-based engine architecture defines patterns and signatures to identify nefarious traffic. The WAF vendor can set the rules, or, as the user, you can customize them to cater to specific security needs. The engine analyzes incoming requests against these rules and decides whether to allow them, block them, or flag them for further inspection.
• Secure sockets layer (SSL)/transport layer security (TLS) termination is used to inspect encrypted traffic. The process decrypts incoming hypertext transfer protocol secure (HTTPS) requests, inspects them for threats, and then re-encrypts them before forwarding them to the web server. In this way, encrypted threats will never bypass the WAF’s scrutiny.
• Anomaly detection is used to identify deviations from normal traffic patterns. It flags or blocks requests that exhibit suspicious behavior.
• All activities are logged, including request time, blocked requests, and permitted traffic. Security audits, recognition of attack patterns, and continuous monitoring of your security posture call for this level of detail.
• Uninterrupted monitoring upholds WAF's reliability, availability, and performance. You collect monitoring data from all parts of your WAF security solution to quickly respond to threats. 
• Web application policies define acceptable use parameters, including input types, access controls, and rate limiting, to ensure that the application only receives legitimate traffic.

How WAFs work

A web application firewall operates at Layer 7 of the open systems interconnection (OSI) model, the application layer. This is the highest layer of the network stack and deals with the actual data being transmitted, such as web pages, emails, and file transfers.

The WAF intercepts all incoming traffic directed toward web apps. It inspects all communication requests before they reach the web server.

The WAF meticulously examines each inbound request and analyzes the content based on predefined security policies and rules for the patterns and characteristics associated with various web application vulnerabilities.

WAFs compare elements within the request (e.g., HTTP headers, parameters, payload) against its security rule set to make it easy to pinpoint suspicious elements within the request.

Supported by a comprehensive suite of cybersecurity rules, WAFs stay vigilant against a spectrum of web application attacks, including:

• SQL injection attacks
• Cross-site scripting (XSS) attacks
  
• Denial of service (DoS) attacks
• Cryptojacking attacks

WAFs also prevent the exploitation of missing security patches, misconfigurations, insecure building practices, and third-party or open-source plugins. However, you can integrate a cloud-based platform that protects against distributed denial of service (DDoS) attacks. If the WAF detects a DDoS attack, it can transfer the traffic to the DDoS protection platform.

WAFs can follow predefined protocols if a request violates a security rule. These actions may involve: 

• Completely stopping the request from reaching the web server.
• Prompting the user for additional verification before allowing the request to proceed.
• Recording the details of the suspicious request for further analysis.

WAFs only work effectively if the security rule set is current. Policies should be regularly updated to cover the latest known attack vectors and vulnerabilities.

WAF vs. Firewalls

While WAFs and traditional network firewalls play a critical role in network security, they target different aspects of network traffic with distinct functionalities. 

For example, organizations that handle credit card data need next-generation firewalls as part of their security measures. While a basic firewall protects the network perimeter, WAFs layer on additional security for web applications that process or store cardholder data to better comply with payment card industry data security standard (PCI DSS) requirements for protecting cardholder data.

WAF traffic inspection methods

WAFs employ various methods to inspect incoming traffic and identify suspicious requests. 

Negative security models: blacklist or blocklist

In this model, all incoming traffic is allowed by default. WAFs then analyze and filter requests against your rules and known harmful patterns (threat signatures). This approach offers quick implementation but has limitations. 

• Ineffective against zero-day attacks: Zero-day attacks have yet to be identified in threat databases, so negative security models can't block what they don't know.
• Susceptible to evasion: Hackers can craft attacks that slightly deviate from known patterns to bypass signature-based detection.
• Limited coverage: Negative security models don’t effectively defend against malware and other attacks, including those listed in the Open Web Application Security Project (OWASP) top 10 web application security risks.

Positive security model: whitelist or allowlist

The positive security model only gives access to the whitelist, aka the allowlist, aka traffic that conforms to predefined safe patterns.

Even though the positive approach provides superior security against zero-day attacks, it requires frequent updates to accommodate new legitimate requests. Modern WAFs can use machine learning and threat intelligence to automate whitelist updates, minimizing manual intervention. 

Contemporary WAFs primarily rely on negative security models or blacklists. For comprehensive protection, WAFs can integrate positive security. This means the requests that pass negative security filters undergo anomaly detection to identify deviations from typical user behavior. If anomalies are found, the traffic source might be blocked or undergo additional scrutiny in subsequent interactions.

A hybrid approach often emerges as the most pragmatic solution. The balance between security and flexibility strengthens your organization's defense against new cyber threats.

WAF blocking mechanisms

WAFs deploy a multi-layered defense strategy against diverse threats. Various blocking mechanisms are discussed here. 

Rate limiting

Rate limiting mitigates DDoS attacks by restricting the requests a user or IP address can submit within a certain time frame. 

WAFs establish a safe threshold for legitimate traffic volume. Any requests that go over this limit from a specific IP address are blocked as a way of preventing attackers from overwhelming the server with a barrage of requests. Users are left with uninterrupted access, and you maintain business continuity by safeguarding servers from overload.

API security

WAFs secure application programming interfaces (APIs) by meticulously filtering requests.  Scrutinizing API requests guarantees adherence to authorized parameters and established authentication protocols. Any deviation from these criteria triggers a blocking response to safeguard APIs from unauthorized access and exploitation.

Bot mitigation

Bot mitigation distinguishes between legitimate users and harmful, automated bots that scrape sensitive data packets or launch credential-stuffing attacks. WAFs employ a combination of techniques to identify malicious bots.

• CAPTCHA challenges present users with puzzles difficult for bots to solve, effectively filtering out automated scripts.
• Bot pretenders mimic legitimate user behavior to deceive bots.
• Web scraping protection identifies and blocks requests characteristic of these activities.
• Bot intelligence employs fingerprints, IP addresses, and behavioral patterns to recognize and thwart malicious bots.

IP fencing

It offers a straightforward approach to blocking requests from known malicious IP addresses. WAFs maintain blacklists of IP addresses associated with prior bad behavior. 

All requests that originate from these blacklisted sources are automatically blocked to prevent repeat attacks. However, this approach relies on a static list of known threats and is vulnerable to new or sophisticated attacks that haven't yet been identified.

Geo-blocking

WAFs restrict access to web applications based on geographical location. The apps can be configured to block requests from specific countries or regions deemed high risk for cyberattacks. Implement this approach with caution to avoid inadvertently blocking legitimate traffic.

Security rules

WAFs analyze incoming requests and compare them against comprehensive security rules to detect and block malicious activity. 

WAFs utilize two primary categories of security rules:

• Predefined rules: The WAF vendor develops these guidelines to protect you against common attack vectors such as SQL injection and XSS.
• Custom rules: These are created by the application owner to address specific security concerns unique to their environment. They provide additional layers of protection beyond the predefined rules, and you can tailor them to the application's specific vulnerabilities.

Anomaly scoring

When a request triggers a rule match, the WAF assigns a score based on the severity of the deviation from the expected behavior. This score contributes to the request's overall risk assessment. Using a risk-based approach, WAFs provide a more enhanced response and reduce the potential for false positives by not blocking every deviation from the norm.

WAF deployment models

3 different types of WAF deployment models can cater to your web application's specific needs and architecture. 

Cloud-based WAFs or host-based WAF

Cloud-based WAFs, delivered as a software as a service (SaaS) model, are a game-changer for businesses seeking total web application security without the burden of managing infrastructure.  

Here's why cloud-based WAFs are ideal for so many organizations.

• Effortless deployment: Cloud-based WAFs offer the fastest and most hassle-free implementation. A simple change to your DNS settings is often all it takes to get started. This is a major advantage, especially for businesses with limited security or IT resources.
• Seamless scalability: Cloud-based WAFs automatically scale up or down to handle fluctuations in traffic volume. This ensures your web application remains protected, even during peak periods, without the need for manual intervention.
• Up-to-date security: Cloud WAF providers constantly update their security rules to stay ahead of the emerging threat landscape. This keeps your web application protected against the latest application layer attack vectors without requiring any action from you.

Cloud-based WAFs are a compelling option for businesses of all sizes. They provide a cost-effective way to achieve enterprise-grade web application security, regardless of your internal security expertise. 

However, it's important to consider potential limitations.

• Customization: Cloud-based WAFs typically offer predefined rules that address common threats. While these rules are highly effective, they may not meet highly specific security needs that require complex custom rules.
• Cost: Generally cost-effective, cloud-based WAF pricing can increase with more complicated security rules and higher web traffic volume.

On-premise WAFs

On-premise WAFs give organizations a high degree of control over their security posture.  You install and manage these WAF solutions directly on your own infrastructure, giving you granular customization options over security rules and configurations.

Here's what makes on-premise WAFs attractive to specific organizations.

• Tailored security: On-premise WAFs let you create and implement customized security rules to address unique threats or vulnerabilities specific to your web applications. This granularity is ideal for organizations with intricate security requirements or those operating in highly regulated industries.
• Data protection: For organizations with strict data privacy risks, keeping security measures entirely on-premise can be a major advantage. On-premise WAFs ensure all traffic inspection and security decisions occur within your own infrastructure, which minimizes potential data exposure risks.

As with all security measures, on-premise WAFs also come with some key considerations.

• Management overhead: Installing, configuring, and maintaining an on-premise WAF requires dedicated IT resources. This includes handling software updates, rule creation, and ongoing security monitoring, which may be a significant burden for organizations with limited IT staff.
• Scalability challenges: Scaling on-premise WAFs to accommodate traffic spikes can be complex and expensive. Adding more hardware resources may be necessary during periods of high traffic, but that can be disruptive and time-consuming.

On-premise WAFs are a strong choice for organizations that prioritize granular control over their security environment and have the resources to manage it properly. They are well-suited for businesses in regulated industries, those with complex security needs, or those with concerns about data privacy.

Hybrid WAFs

Hybrid WAFs draw from the strengths of both cloud-based and on-premise deployments. Here's how they can share responsibilities to provide a comprehensive security posture.

• It can be more economical than a purely on-premise solution, as cloud-based WAFs handle common threats efficiently.
• Cloud WAFs seamlessly scale to accommodate traffic spikes, while on-premise WAFs can be dedicated to critical applications.
• The combination provides layered security, with cloud WAFs taking care of common threats and on-premise WAFs offering additional protection for sensitive applications. But you must consider that it requires managing cloud and on-premise components, potentially increasing complexity.

The optimal WAF deployment model depends on your organization's security needs, technical expertise, and budget. Cloud-based WAFs are popular for their simplicity and scalability, on-premise WAFs offer greater control, and hybrid deployments balance both approaches.

Limitations of WAFs

While web application firewalls are powerful security tools, they have limitations to consider.

• Zero-day attacks: WAFs rely on predefined rules to identify threats. Zero-day attacks, which exploit previously unknown vulnerabilities, can bypass WAFs.
• Complex application logic: Complex application logic with intricate functionalities can be challenging for WAFs to understand. The lack of understanding could lead to missed threats hidden within legitimate-looking requests.
• False positives: WAFs can mistakenly flag legitimate traffic as malicious, which causes disruptions and requires manual intervention.
• Performance impact: WAFs add some processing overhead, potentially affecting application performance, especially for high-traffic websites.
• Configuration complexity: WAFs require careful configuration to do their work. Improper configuration renders them useless and can even introduce security vulnerabilities.

Prevention is better than a cure

Understanding how a web application firewall works is just the first step. This knowledge empowers you to choose a WAF tailored to your application and implement ongoing monitoring for optimal protection.  

By being proactive, you can transform your WAF from a basic security measure into a powerful shield against cyberattacks. Don't wait for a breach - take action now!

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