CVE-2026-4266 WatchGuard Firebox Insecure Deserialization in Fireware Access Portal

What is CVE-2026-4266?

CVE-2026-4266 is a high-severity unsafe deserialization vulnerability in Watchguard Fireware, published on 30 Mar 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

An Insecure Deserialization vulnerability in WatchGuard Fireware OS allows an attacker that has obtained write access to the local filesystem through another vulnerability to execute arbitrary code in the context of the portald user.

Note, this vulnerability does not affect Firebox platforms that do not support the Access Portal feature, including the T15 and T35.

Weakness: CWE-502

Which versions are affected by CVE-2026-4266?

It affects 1 product.

Products include Watchguard Fireware.

How do I fix CVE-2026-4266?

No fix has been published for CVE-2026-4266 yet. Limit exposure of the affected software until one is available.

Upgrade, and only deserialise data from trusted sources or with an allow-list of types. More about Unsafe deserialization.

Is CVE-2026-4266 being exploited?

There is no known exploitation of CVE-2026-4266 in the wild and no public exploit code.

Other vulnerabilities in Watchguard Fireware

• CVE-2022-26318 WatchGuard Firebox and XTM Appliances Arbitrary Code Execution Exploited Critical 9.8
• CVE-2025-14733 WatchGuard Firebox Out of Bounds Write Exploited Critical 9.3
• CVE-2025-9242 WatchGuard Firebox Out-of-Bounds Write Exploited Critical 9.3
• CVE-2022-23176 WatchGuard Firebox and XTM Privilege Escalation Exploited High 8.8
• CVE-2022-31789 Integer overflow in n/a Critical 9.8

All Watchguard Fireware vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-mmhr-mfjp-vv8j.