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

• Severity: medium (CVSS 6.7 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-03-30 · updated 2026-08-28
• Weakness: CWE-502

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.

Affected products

• WatchGuard Fireware OS: from 2025.1 before 2026.2; from 12.1 before 12.12 — fixed in 12.12, 2026.2

How to fix

Upgrade to a fixed version: WatchGuard Fireware OS 12.12, 2026.2. Check the vendor advisory for mitigations.

References

• https://psirt.watchguard.com/CVE-2026-4266
• https://www.watchguard.com/wgrd-psirt/advisory/wgsa-2026-00007

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