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How to Assess and Audit Firewall Security
Checking firewall security is one of the most critical steps in protecting your organization’s network, data, and systems. A firewall is often the first line of defense between your internal infrastructure and external threats. However, misconfigurations, outdated firmware, or weak policies can turn it into a major vulnerability.
OC Security Audit Company helps your business find the vulnerabilities in your network, assess the level of security of your network, and works with you, your team, and your MSP to enhance the security level of your data and information.
With over 25 years of experience in cybersecurity assessment, network security, and data information security audits, OC Security Audit leadership holds certifications including CCISO, CISSP, MCSE Security, CCNP, CCNA, MCSA Security, and MCITP. Based in Orange County, California, we support businesses across the country both on-site and remotely.
Checking Firewall Security
Checking firewall security is the structured process of reviewing, validating, and testing firewall configurations, rules, policies, and operational controls to ensure they properly protect the organization.
This includes:
Reviewing inbound and outbound firewall rules
Validating network segmentation and zone design
Checking administrative access controls
Verifying logging and monitoring configurations
Ensuring firmware and security patches are current
Testing exposure from internal and external perspectives
The goal is to confirm that only authorized traffic is allowed and that all other traffic is blocked, logged, and monitored.
Main Security Vulnerabilities in Firewalls
The most common firewall-related vulnerabilities include:
Overly permissive firewall rules (e.g., Any-to-Any access)
Exposed management interfaces accessible from the internet
Unpatched firewall firmware or VPN modules
Weak administrator passwords or lack of MFA
Poor network segmentation (flat network design)
Misconfigured NAT or port forwarding rules
Disabled or insufficient logging
Insecure VPN configurations
Legacy protocols enabled (e.g., Telnet, SNMPv2)
Stale, unused, or undocumented firewall rules
These weaknesses can provide attackers with direct access, lateral movement opportunities, or stealth persistence.
Main Tasks IT Teams Should Perform to secure firewalls
To ensure firewall security, IT teams should perform the following core tasks:
1. Implement Least Privilege
Remove broad rules and restrict access to specific IP addresses, ports, and services.
2. Restrict Administrative Access
Allow firewall management only from dedicated admin networks or secure VPN with MFA.
3. Enable Multi-Factor Authentication
All firewall administrator accounts must require MFA.
4. Patch Regularly
Keep firewall firmware and security services updated.
5. Review Rules Periodically
Conduct quarterly rule reviews and remove unused or duplicate entries.
6. Enable Centralized Logging
Send firewall logs to a SIEM or centralized logging system.
7. Test External Exposure
Perform external vulnerability scans to ensure only intended services are exposed.
8. Secure VPN Configuration
Use strong encryption and disable outdated protocols.
9. Backup Configurations
Securely store firewall configuration backups and test restoration procedures.
10. Conduct Independent Security Audits
Engage third-party security professionals to validate your firewall posture objectively.
Hacking Strategies and Techniques That Exploit Firewall Weaknesses
Attackers commonly use the following strategies:
Port scanning to identify exposed services
Brute force and password spraying against VPN portals
Exploiting unpatched firewall vulnerabilities
Leveraging overly permissive outbound rules for command-and-control communication
Exploiting misconfigured port forwarding rules
Lateral movement across poorly segmented networks
Credential reuse from leaked password databases
Phishing administrators to gain firewall access
Tunneling traffic through allowed services (DNS/HTTPS)
Log tampering after gaining administrative access
These techniques are often automated and continuously scanning the internet for vulnerable firewalls.
20-Point Firewall Security Audit Checklist
1. Remove Any-to-Any Rules
Importance: Critical
Risk Level: High
If left open, attackers can access internal services directly.
It allows unrestricted traffic into sensitive systems.
It significantly increases the attack surface.
2. Disable Public Management Access
Importance: Critical
Risk Level: High
Exposed admin portals are prime targets.
Attackers scan continuously for firewall login pages.
Brute-force or exploit attempts become easy.
3. Enable Multi-Factor Authentication for Admins
Importance: Critical
Risk Level: High
Stolen credentials alone would grant access.
MFA prevents credential reuse attacks.
Without it, phishing leads to full compromise.
4. Keep Firmware Updated
Importance: Critical
Risk Level: High
Unpatched firewalls are frequently exploited.
Attackers use known CVEs for remote execution.
Delayed patching increases exposure window.
5. Restrict VPN Access by IP or Policy
Importance: High
Risk Level: High
Open VPN portals invite password attacks.
Geographic restrictions reduce attack attempts.
Unrestricted access enables brute-force campaigns.
6. Enforce Strong Password Policies
Importance: High
Risk Level: High
Weak passwords are easily cracked.
Credential stuffing becomes successful.
Admin takeover becomes likely.
7. Implement Network Segmentation
Importance: Critical
Risk Level: High
Flat networks allow lateral movement.
One compromised device exposes all systems.
Segmentation limits breach impact.
8. Enable Intrusion Prevention (IPS)
Importance: High
Risk Level: Medium
IPS detects known attack patterns.
Without it, exploit attempts go unnoticed.
Malicious traffic flows freely.
9. Centralize Logs
Importance: High
Risk Level: Medium
Local logs can be deleted by attackers.
SIEM enables detection of anomalies.
Without logs, investigations fail.
10. Remove Unused Rules
Importance: Medium
Risk Level: Medium
Stale rules create hidden exposure.
Attackers exploit forgotten access paths.
Complex rule sets hide weaknesses.
11. Disable Legacy Protocols
Importance: High
Risk Level: Medium
Protocols like Telnet transmit plaintext credentials.
Attackers can intercept credentials.
Encryption-less services weaken defenses.
12. Limit Outbound Traffic
Importance: High
Risk Level: Medium
Malware needs outbound communication.
Open egress allows data exfiltration.
Command-and-control traffic goes undetected.
13. Secure SNMP Configuration
Importance: Medium
Risk Level: Medium
Default community strings are widely known.
Attackers gather network intelligence.
Configuration data may leak.
14. Backup Firewall Configuration
Importance: Medium
Risk Level: Medium
Ransomware may corrupt configs.
Without backups, recovery is delayed.
Attackers may alter rules silently.
15. Monitor Failed Login Attempts
Importance: High
Risk Level: Medium
Repeated login failures indicate brute-force attempts.
Without monitoring, attacks continue unnoticed.
Admin accounts become compromised.
16. Restrict Administrative Roles
Importance: High
Risk Level: Medium
Shared admin accounts reduce accountability.
Compromise affects all privileges.
Role-based access limits exposure.
17. Validate Port Forwarding Rules
Importance: High
Risk Level: High
Improper NAT exposes internal servers.
Attackers exploit unintended services.
Shadow IT becomes externally reachable.
18. Conduct Regular Vulnerability Scans
Importance: High
Risk Level: Medium
Unidentified weaknesses remain open.
External attackers discover them first.
Routine scanning closes gaps early.
19. Implement Change Control Procedures
Importance: Medium
Risk Level: Medium
Unauthorized changes weaken policies.
Errors go undocumented.
Rollback becomes difficult.
20. Perform Independent Security Audit
Importance: Critical
Risk Level: High
Internal bias overlooks weaknesses.
Third-party assessment reveals blind spots.
Attack paths are validated realistically.
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