How WAFs Differ from Intrusion Prevention Systems (IPS)

Web Application Firewall (WAF) and Intrusion Prevention System (IPS) are two crucial cybersecurity technologies designed to protect applications and networks from attacks. While both serve as defense mechanisms, they differ significantly in their scope, functionality, and use cases.

WAFs protect web applications by filtering HTTP/HTTPS traffic, while IPS monitors and inspects network traffic to detect and block threats. Let’s explore the key differences between WAF and IPS, their capabilities, and when to use each.

What is a Web Application Firewall (WAF)?

A Web Application Firewall (WAF) is designed to protect one’s web applications by monitoring and filtering the HTTP/HTTPS traffic between their website and the internet. It operates at the application layer (Layer 7) of the OSI model and is specifically tailored to detect and mitigate threats that target web applications.

Its primary function is to block common web-based attacks such as SQL injections, cross-site scripting (XSS), and other application-specific threats.

A WAF operates by applying predefined rules and AI-driven analysis to incoming traffic, identifying and blocking malicious requests before they reach web servers. AI enhances detection by analyzing behavior, mitigating zero-day threats, and adapting to evolving attack patterns in real time.

Discover how a WAF filters, detects, and blocks threats in our blog on How a WAF Works

What is an Intrusion Prevention System (IPS)?

An Intrusion Prevention System (IPS) is a network security solution designed to detect and prevent threats targeting the underlying network infrastructure. It operates at Layer 3 and Layer 4 of the OSI model, analyzing network traffic for malicious patterns.

IPS works by analyzing network traffic patterns and comparing them against known threat signatures or anomalous behaviors. When it identifies suspicious activity—such as a network-based attack or an unauthorized access attempt—it can take immediate action to block the threat. The main goal of an IPS is to provide comprehensive network security, ensuring that threats are intercepted before they can spread or cause significant damage.

How WAFs Differ from Intrusion Prevention Systems (IPS)

Layer of Protection: Network vs. Application

IPS is effective at detecting and blocking attacks such as port scans, brute-force login attempts, and known exploits targeting network protocols. However, because an IPS does not inspect the full HTTP request structure, it cannot effectively identify sophisticated web-based attacks like SQL injection or cross-site scripting (XSS).

In contrast, a WAF operates at the application layer (Layer 7), where it analyzes HTTP/S traffic and interprets user requests, URLs, and payloads. This deeper inspection allows it to detect and block threats that specifically target web applications, such as API abuse, session hijacking, and other vulnerabilities listed in the OWASP Top 10. By understanding web application logic, a WAF can enforce security policies that prevent malicious requests from reaching the backend server.

Threat Detection: Signature-Based vs. Behavioural Analysis

One major limitation of IPS is that it primarily relies on signature-based detection. It uses predefined patterns to identify known threats. This limitation makes IPS ineffective against evolving threats that do not have a documented attack pattern.  When a zero-day vulnerability is discovered, IPS cannot provide immediate protection until a vendor releases a security update.

WAF on the other hand, incorporates behavioral analysis, anomaly detection, and custom security rules to defend against emerging threats. They can identify suspicious activities that deviate from normal application behavior, allowing them to mitigate attacks even when no predefined signature exists. For instance, if an attacker attempts SQL injection with a payload that does not match an existing IPS signature, the WAF can still block the request based on the context and structure of the query.

Additionally, virtual patching at the WAF level, ensures vulnerabilities are patched, offering immediate protection before official patches are available. This proactive security approach minimizes the window of exposure and keeps applications secure against zero-day threats. Explore how AppTrana WAF ensures autonomous patching in 72 hours with SwyftComply here.

Encrypted Traffic Handling

Another key limitation of IPS is its inability to effectively inspect encrypted traffic. Since advanced web applications use HTTPS to secure communications, most of the data passing through an IPS is encrypted. Without SSL/TLS decryption capabilities, an IPS cannot analyze the contents of HTTPS requests, making it blind to application-layer attacks.

A WAF, however, is designed to decrypt and inspect HTTPS traffic before forwarding requests to the web server. This allows it to analyze the full HTTP request and response, detecting malicious payloads hidden within encrypted communication. This capability is critical for defending against threats like encrypted malware delivery, hidden parameter tampering, and API abuse.

False Positives and Customization: IPS vs. WAF Flexibility

IPS devices often generate a high number of false positives due to their broad detection methods. Since they are primarily tuned for network-based threats, they may block legitimate application traffic if it exhibits behavior similar to an attack pattern. Adjusting an IPS to reduce false positives requires extensive fine-tuning, which can be complex and time-consuming.

Managed WAFs like AppTrana offer greater flexibility in rule customization. Security teams can create tailored rules that align with specific application requirements, reducing the chances of blocking legitimate traffic. Additionally, advanced WAF solutions provide automated threat intelligence updates, allowing them to adapt to new attack vectors without requiring constant manual intervention.

Deployment and Use Case Scenarios

IPS solutions are typically deployed at the network perimeter, where they act as an inline security appliance, analyzing all traffic entering and leaving the network. This makes them effective for enterprises that need to protect their infrastructure from broad intrusion attempts, malware propagation, and denial-of-service (DoS) attacks. However, IPS does not provide targeted protection for web applications, leaving critical application-layer vulnerabilities exposed.

A WAF(WAAP), in contrast, is specifically designed to protect web applications and APIs. It can be deployed as a cloud-based service or an on-premises appliance. Businesses that rely on web-based services, e-commerce platforms, and customer-facing portals benefit from WAF protection, as it defends against threats that traditional IPS solutions cannot mitigate.

WAF vs. IPS: Key Differences

Feature	WAF	IPS
Layer of Protection	Application Layer (Layer 7)	Network & Transport Layer (Layer 3 & 4)
Scope of Protection	Specializes in protecting web applications by filtering HTTP/HTTPS traffic	Provides broader protection by monitoring all network traffic
Primary Focus	Web applications	Network infrastructure
Threats Addressed	OWASP Top 10, bot attacks, API abuse	Network intrusions, DoS, malware
Detection Method	Signature-based, behavioral, and anomaly detection	Signature-based and anomaly detection
Placement	In front of web servers	Between firewall and internal network
Customization	Highly customizable rules for application logic	Less customizable, relies on predefined rules
Virtual Patching	Yes, for web vulnerabilities	No
Integration	Works with CDNs, load balancers, and SIEMs	Integrates with firewalls and endpoint security

 

Conclusion

Both WAFs and IPS contribute to cybersecurity by addressing different threat vectors. Implementing the right solution depends on an organization’s security needs, ensuring comprehensive protection against evolving cyber threats. When it comes to protecting web applications, WAFs provide more focused and effective defenses, offering a slight edge over IPS for organizations that depend heavily on web-based services.