As we all know, firewalls are the absolute backbone of network security defenses. By filtering incoming and outgoing traffic, they prevent attacks like denial-of-service (DoS) and intrusions from directly reaching our applications. However, firewalls have their limitations - and relying solely on them leaves apps open to compromise.
Whether it be through misconfigurations or even just inherent design flaws, there are several “loopholes” that may allow threats to bypass firewall security. And any attacks that successfully penetrate your applications can lead to data destruction, theft, service outages, and huge financial and reputational damages for businesses.
With this in mind, this article outlines some of the major firewall vulnerabilities that exist today, before providing some pragmatic solutions to harden your app defenses. Applying these firewall best practices as part of an integrated, layered security strategy will significantly improve application resilience, and hopefully, your peace of mind.
Addressing A Few Misconceptions Around Firewalls
Many people (yes, even experienced devs) incorrectly assume firewalls provide full application protection. But the truth is that traditional firewalls only tend to filter lower-level network protocols and traffic at perimeter chokepoints. They lack deep insight into layered application architectures and encrypted sessions between components.
Nor can firewalls fully protect against attacks targeting applications themselves – like SQL injections, cross-site scripting (XSS), broken authentication, etc. These application-layer threats employ valid protocols and sessions to penetration defenses.
Proper configuration is also critical. Overly permissive rules, legacy designs allowing unnecessary traffic flows, and outdated firmware leave security gaps. Attackers actively probe for these sorts of weaknesses using firewall scanning tools.
Top Firewall Vulnerabilities
Okay, so let's now run through some of the main vulnerabilities faced by firewalls, a few of which we have just touched upon.
1. Misconfiguration
The number one firewall risk comes from poor device and ruleset configuration. Complex environments with thousands of restrictive policies are prime targets. That’s because a single misconfiguration can have catastrophic impacts, allowing attackers access to backend databases, cloud services, or other sensitive resources. Common issues include:
- Overly permissive rules between app tiers that expose vulnerabilities. Restrict access to only required ports and protocols based on zero trust principles. This helps limit lateral attack movement when parts of your architecture get compromised.
- Failure to update rulesets as environments change. Review firewall policies regularly to remove unnecessary access as apps scale or infrastructure gets retired.
- No central management. Use firewall management platforms to sync allow lists across devices, and automatically push updated rulesets. Avoid manually configuring firewalls whenever possible – humans make mistakes and you need to have processes in place to mitigate these risks.
- Not upgrading firmware and security patches. New vulnerabilities like remote code executions surface frequently. Aggressively patch perimeter firewalls to close loopholes before attackers can discover and weaponize them.
2. Encrypted Traffic & Evasion
While firewalls filter plain text network traffic via signatures and blacklists, encryption and obfuscation let malware sneak by. HTTP, TLS, and SSH encryption hide payloads from inspection. Polymorphic malware and file-less attacks also morph patterns to avoid detection. Solutions include:
- Decryption. Deploy SSL inspection to decode outbound HTTP traffic and reveal threats.
- Sandboxing. Detonate suspicious files in isolated sandboxes to force malicious behavior and detection.
- Behavioral analytics. Inspect network traffic patterns for signs of compromise like unusual connection spikes, even if payloads stay encrypted.
3. Application-Layer Attacks
Standard firewalls focus on filtering lower network layers. But threats targeting the application layer itself can penetrate to backend systems. Attackers typically access apps legally and then exploit logic flaws to steal and destroy data. Common examples of this include:
- SQL injection: Manipulating input fields to access or corrupt databases.
- XSS: Injecting JavaScript payloads to steal site privileges or user sessions.
- Application DoS: Overwhelming apps with junk data to crash software and servers.
Such application payloads craft messages staying within permitted protocols. While firewalls might detect volume-based network floods, tailored requests avoid detection.
4. Zero-Day Threats & Advanced Evasions
The ultimate firewall bypasses take advantage of zero-day exploits – attacks using previously unknown software vulnerabilities with no current fixes or signatures. With no patches available, zero-days are completely invisible to perimeter defenses. Attackers often chain together multiple zero-days to penetrate layered app infrastructure before vendors can respond. Advanced evasion techniques also dupe firewalls, including:
- IP Fragmentation: Breaking malicious payloads into small pieces to avoid detection.
- HTTP Parameter Pollution: Using duplicated query string variables to confuse web application firewalls (WAFs).
- Protocol Impersonation: Wrapping attacks in permitted protocols like HTTPS to bypass port filtering.
5. Social Engineering
Of course, this list would be incomplete without us mentioning the greatest weakness to any security posture, human beings. Today, hackers increasingly rely on social engineering, phishing, email fraud, and deception tactics to manipulate users into handing over critical information, thus bypassing firewalls and any systems in place.
Internal staff granting unnecessary network access, failing to vet suspicious links, or even physically carrying malware past checkpoints undermine firewalls every day.
Strengthening Application Defenses Beyond Traditional Firewalls
While traditional firewalls serve an important role in filtering lower-level network traffic, as we've discussed, today's complex application environments require a more holistic approach to security – spanning far beyond just perimeter firewalls. Here are a few quick tips to better protect your apps:
- Zero Trust Architecture: Adopt zero trust principles that verify and authorize all access requests - whether on-premise or from the cloud. This limits the attack blast radius when parts of an app get breached. Microsegmentation, API gateways, and privilege controls are key zero-trust components.
- Web Application Firewall (WAF): Deploy a WAF to filter inbound HTTP application traffic at edge locations. WAFs specialize in detecting and blocking attacks targeting web-based apps and APIs. Integrate WAF events with security analytics for greater threat visibility.
- RASP: Implement runtime application self-protection to detect and respond to threats targeting apps in production environments. RASP uses agents to analyze memory, configs, and traffic flows from inside running applications.
- Sandboxing: Detonate suspicious files, links, and scripts in isolated sandboxes. This reveals malicious behavior by executing code safely away from production networks.
- Access Controls: Strictly limit application access to authorized user groups and systems. Disable unnecessary application functionality, ports, services, and local resource access to reduce the attack surface.
Final Word
In the end, thinking beyond firewalls is crucial when architecting layered defenses for modern application environments – especially business-critical software facing the public internet. As such, combining traditional network security with application-aware controls, behavior monitoring, and advanced threat detection techniques helps identify and stop attacks that bypass firewalls alone.
Revisit access policies and system interconnections regularly as new risks emerge. And never forget the human element! Train internal teams on secure practices to close firewall gaps from inside your networks too.
