High [CVE-2026-4266] WatchGuard Firebox Insecure Deserialization in Fireware Access Portal
This high-severity WatchGuard advisory covers CVE-2026-4266 affecting Fireware OS.
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Summary
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.
- Fireware OS 2025.1 before 2026.2
- Fireware OS 12.1 before 12.12
- Fireware OS 12.1 before 12.11.9
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
- 2026.2
- 12.12
- 12.11.9
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
Mitigation
Upgrade to a fixed release: 2026.2, 12.12, 12.11.9. That is the remediation for this advisory.
The vendor advisory may list additional interim mitigations or workarounds not captured here — review it before change work.
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
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