Why Legacy WatchGuard VPN Vulnerability Still Put Companies at Risk

Key Takeaways

• A critical WatchGuard Firebox VPN vulnerability (CVE-2025-9242) is being actively exploited, even on systems where outdated VPN configurations were “deleted.”

• The flaw allows remote, unauthenticated code execution through the iked process, giving attackers direct control of the firewall.

• Legacy VPN configuration remnants create hidden security risks, highlighting a broader issue across major vendors like Cisco, Fortinet, and Palo Alto.

• Organizations must perform regular VPN configuration audits, apply patches quickly, enable advanced monitoring, and validate that old tunnels are fully removed.

• Tanner Security helps companies uncover hidden VPN vulnerabilities through expert network penetration testing and VPN configuration reviews.

Introduction to WatchGuard VPN Vulnerability

In October 2025, cybersecurity researchers discovered something alarming: a critical flaw in WatchGuard VPN Vulnerability with the Firebox (CVE-2025-9242) devices was being actively exploited in the wild. What made this vulnerability stand out wasn’t just its severity, but how it lingered, even after companies thought they had fixed it.

Many IT administrators believed that deleting old VPN configurations would eliminate the risk of security breaches. Unfortunately, that wasn’t the case. Even after removal, remnants of these configurations could still leave systems exposed. This hidden vulnerability highlights a broader and ongoing issue: legacy VPN configurations that refuse to die quietly.

It’s a reminder that in cybersecurity, deleting doesn’t always mean secure. Understanding why these risks persist and how to address them is crucial for any organization that relies on VPNs for remote work or site-to-site connections.

The WatchGuard Firebox Vulnerability Explained

At the center of this issue is an out-of-bounds write vulnerability in the Fireware OS, specifically within the iked process that manages IKEv2 VPN connections. In plain terms, this flaw allows remote attackers to send specially crafted data to the device, thereby gaining the ability to run malicious code on the firewall itself without requiring authentication.

That means attackers don’t need credentials or internal access. All it takes is the right packet sent to the right target. Once exploited, the attacker effectively controls the organization’s first line of defense.

The Problem with “Deleted” Configurations

Here’s where things get tricky. WatchGuard found that even when administrators removed specific IKEv2-based VPN configurations, the vulnerability could remain. If another VPN tunnel (for example, one using a static gateway) was still active, traces of the vulnerable configuration might persist under the surface.

In other words, the system’s visible settings could look clean, but the underlying processes still carried the weakness. It’s like removing a virus from your computer’s desktop but leaving it active in the background.

This situation creates a dangerous illusion of safety. IT teams mark the issue as resolved, believing they’ve mitigated the risk, while attackers continue to exploit the leftover configuration code that was never truly disabled.

Why Legacy Configurations Stick Around

Network appliances aren’t simple systems. They rely on complex layers of code, shared libraries, and interdependent services. When one configuration is removed, shared components often remain active because other services use them.

Add in years of updates, different administrators, and piecemeal documentation, and it’s easy to see how remnants pile up. Over time, this creates what’s known as configuration residue, which is leftover settings and processes that still run behind the scenes.

Unfortunately, many devices don’t provide deep visibility into these internal states. The management interface shows only what’s active on the surface, not what’s quietly running under the hood.

Signs You Might Be Under Attack

WatchGuard shared several indicators that companies can use to spot signs of exploitation:

• Unusually large IDi payloads in IKE_AUTH request messages (greater than 100 bytes). These appear in diagnostic logs and almost always indicate a malicious attempt.
• Hangs or crashes in the iked process. If VPN connectivity drops suddenly or users can’t reconnect, it could signal an active exploit attempt.

Companies should enable error-level logging and regularly monitor their Fireboxes for these patterns. Even one abnormal log entry should trigger immediate investigation.

The Bigger Picture: Hidden Risks Across All Vendors

Although WatchGuard’s flaw brought this issue into focus, the problem isn’t unique to them. Similar cases have been reported in products from Cisco, Fortinet, Palo Alto Networks, and others.

The root cause is the same everywhere: decades of accumulated technical debt. As vendors add new features, patches, and integrations, systems grow more complex. Old configurations linger, often invisible but still active, creating a patchwork of potential vulnerabilities.

For businesses that have evolved their networks over many years, it’s common to find outdated or partially removed configurations that continue to shape how the infrastructure behaves.

Best Practices for Securing VPN Configurations

• Conduct Regular Configuration Audits: Audit your VPN settings frequently. Document every connection, review historical configurations, and confirm that decommissioned tunnels are truly gone, not just hidden.
• Verify Configuration Removal: When removing a VPN, don’t stop at the management console. Check running processes, logs, and system states to ensure optimal performance. Contact the vendor if necessary to confirm full removal.
• Stay Current on Patching: Always apply critical patches as soon as they’re available, especially when active exploitation is confirmed. Waiting even a few days can dramatically increase your risk.
• Enhance Monitoring and Alerts: Enable detailed diagnostic logging and set up alerts for suspicious behavior, such as unusual payload sizes or repeated failed VPN negotiations.
• Implement Version Control for Configurations: Track every configuration change through version control or change management systems to ensure accurate and transparent record-keeping. This creates a historical record, making it easier to identify anomalies or rollback errors.
• Test Security Controls Regularly: Conduct periodic penetration tests or vulnerability assessments that focus on VPN infrastructure. These assessments often uncover overlooked risks that automated scans miss.

Building a Proactive Security Mindset

Many businesses still approach security reactively, patching when something goes wrong or when vendors sound the alarm. That mindset isn’t enough anymore.

A proactive approach means:

• Regularly reviewing security configurations.
• Continuously monitoring for indicators of compromise.
• Conducting routine penetration tests and configuration reviews.
• Training IT staff to understand how “legacy” systems can create modern risks.

Cybersecurity isn’t just about responding to alerts—it’s about understanding your environment deeply enough to anticipate where threats might emerge next.

WatchGuard VPN Vulnerability Conclusion

The WatchGuard Firebox vulnerability revealed a hard truth: outdated or incomplete VPN configurations can expose your company even when you think they’re gone.

Deleting a configuration doesn’t guarantee safety. Residual processes, shared code paths, and years of technical complexity can leave behind exploitable traces that attackers know how to find.

Protecting your company requires more than patching devices; it demands continuous auditing, validation, and vigilance. As attackers become faster and more sophisticated, proactive configuration management and regular security assessments are important.

If your company hasn’t reviewed its VPN configurations recently, now is the time to start. Contact our Network Penetration Testing team at Tanner Security to get your VPN configuration review today. The threats are active, the risks are real, and as the WatchGuard case shows, what you can’t see can still hurt you.