Positive Security vs. Negative Security: A Comparison Using F5's Security Portfolio

In the world of cybersecurity, understanding different approaches to threat mitigation is critical. Two fundamental security strategies often discussed are positive security and negative security. Both methods aim to protect applications, but they do so in contrasting ways. This post will explore these concepts using products in the F5 portfolio, particularly focusing on Web Application and API Protection (WAAP) solutions, such as F5 BIG-IP Advanced WAF, F5 Distributed Cloud WAAP and F5 NGINX App Protect.

 

What is Positive Security?

The positive security model is often referred to as a "default deny" model. It allows only known, trusted traffic, blocking everything else unless explicitly allowed. The idea is to trust a predefined list of "good" behaviors while blocking any unexpected or abnormal traffic.

Key Features of Positive Security:

• Whitelisting: A whitelist is created based on known safe entities (IP addresses, users, behaviors, etc.), and only these are allowed access.
• Strict Enforcement: Any traffic that deviates from the defined norms is blocked.
• Reduced Attack Surface: Because only permitted actions are allowed, the potential for exploiting unknown vulnerabilities is minimized.

 

F5 Implementation of Positive Security

F5 BIG-IP Advanced WAF, F5 Distributed Cloud WAAP and NGINX App Protect employ positive security techniques, especially through custom security policies. These policies are based on the specific needs of the application and can be fine-tuned to only allow desired inputs and behaviors.

• Application Layer Protection: BIG-IP Advanced WAF can block traffic that doesn't conform to predefined application rules, allowing only legitimate users to interact with the app.
• Automated Learning Mode: Advanced WAF offers a learning mode where it can automatically profile the application, identify typical behaviors, and suggest a positive security model.
• Layer 7 DDoS Mitigation: The positive security model also helps block malicious Layer 7 traffic by identifying and allowing only legitimate request patterns.

F5 Distributed Cloud WAP: Employs positive security techniques by enabling strict traffic rules based on user behavior analytics and advanced bot detection.

• API security feature, you can lock down APIs to accept only specific, defined inputs, making it much harder for attackers to exploit vulnerabilities.

 

What is Negative Security?

The negative security model works as a "default allow" model, where all traffic is allowed unless it matches a defined list of malicious behaviors. Essentially, this strategy relies on blocking known bad entities (e.g., IP addresses, signatures of attacks, etc.).

Key Features of Negative Security:

• Blacklisting: A blacklist contains signatures or patterns of known attacks, and traffic matching these signatures is blocked.
• Flexibility: Since most traffic is allowed unless it is identified as harmful, this model is more flexible but often less secure.
• Signature-Based Detection: Most negative security systems depend on an updated list of attack signatures, such as SQL injection, cross-site scripting (XSS), and other known vulnerabilities.

 

F5 Implementation of Negative Security

F5 products incorporate negative security practices, particularly through signature-based protections.

• BIG-IP ASM: The Application Security Manager (ASM) module of F5 offers robust signature-based detection for common vulnerabilities like SQL injection and XSS.
• Predefined Attack Signatures: BIG-IP WAFs come preloaded with a vast library of attack signatures, making it easier to block known threats.
• Real-Time Updates: Regular updates to threat intelligence ensure that new and emerging threats are quickly blacklisted.
• Distributed Cloud: It leverages bot mitigation using a negative security approach, where known bot signatures and behaviors are automatically blocked.

 

Positive Security vs. Negative Security: Which to Choose?

Both approaches have their merits and limitations, and the best choice depends on the specific application and environment.

• Positive Security:
• Pros: Highly effective for sensitive applications like banking or healthcare, where only specific actions should be permitted.
• Cons: Requires meticulous configuration and constant monitoring, as it can block legitimate traffic if not properly tuned.
• Negative Security:
• Pros: Easier to implement and maintain since it focuses on blocking only known threats. Better suited for less critical applications where flexibility is key.
• Cons: Leaves the application vulnerable to zero-day attacks or new threats that haven't been blacklisted yet.

 

Hybrid Approach with F5 Products

One of the strengths of F5’s WAF solutions is the ability to combine both positive and negative security models for a hybrid approach.

• F5 BIG-IP Advanced WAF allows organizations to implement both positive security (through custom policies and traffic shaping) and negative security (using signature-based detection). This ensures comprehensive coverage by blocking known threats while also enforcing strict access controls.
• NGINX App Protect also offers flexibility by supporting both models, allowing businesses to optimize their security posture based on the application’s requirements.
• Distributed Cloud WAAP not only supports a hybrid model but it provides security services via a SaaS consumption model. Additionally, the platform addresses the growing complexity of managing applications across multiple environments—public clouds, private data centers, and edge locations.

 

Conclusion

In a modern, dynamic security landscape, both positive and negative security models play vital roles. Positive security offers a strong defense for highly sensitive applications by allowing only trusted behaviors, while negative security provides broader coverage against known threats. F5 products, such as BIG-IP Advanced WAF, Distributed Cloud F5 Distributed Cloud WAAP, and NGINX App Protect, empower organizations to choose the best model or combine both, ensuring a tailored, effective security strategy.