CVE-2026-4266

WatchGuard Firebox Insecure Deserialization in Fireware Access Portal

MEDIUM

6.7

CVSS Score

Published: March 30, 2026 at 12:38 PM UTC

Updated: August 28, 2026 at 12:18 AM UTC

37 products affected across 1 vendorFirewareFirebox T55Firebox M4800

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Severity

MEDIUM6.7

Exploit prediction

EPSS 0.3%

SSVC

No known exploit

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.This issue affects Fireware OS: 12.1 through 12.11.8 and 2025.1 through 2026.1.2. Note, this vulnerability does not affect Firebox platforms that do not support the Access Portal feature, including the T-15 and T-35.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Fireware · WatchGuard

95%

12.1 ≤ v < 12.11.912.1 ≤ v < 12.122025.1 ≤ v < 2026.212.1 2025.1

Affected range stops below 12.11.9, so it looks safe — our inference, not a vendor statement

Affected range stops below 12.12, so it looks safe — our inference, not a vendor statement

Affected range stops below 2026.2, so it looks safe — our inference, not a vendor statement

watchguard-firebox-cloud (environment) · watchguard-firebox-m270 (environment) · watchguard-firebox-m290 (environment) · watchguard-firebox-m295 (environment) · watchguard-firebox-m370 (environment) · watchguard-firebox-m390 (environment) · watchguard-firebox-m395 (environment) · watchguard-firebox-m440 (environment) · watchguard-firebox-m4600 (environment) · watchguard-firebox-m470 (environment) · watchguard-firebox-m4800 (environment) · watchguard-firebox-m495 (environment) · watchguard-firebox-m5600 (environment) · watchguard-firebox-m570 (environment) · watchguard-firebox-m5800 (environment) · watchguard-firebox-m590 (environment) · watchguard-firebox-m595 (environment) · watchguard-firebox-m670 (environment) · watchguard-firebox-m690 (environment) · watchguard-firebox-m695 (environment) · watchguard-firebox-nv5 (environment) · watchguard-firebox-t115-w (environment) · watchguard-firebox-t125 (environment) · watchguard-firebox-t125-w (environment) · watchguard-firebox-t145 (environment) · watchguard-firebox-t145-w (environment) · watchguard-firebox-t185 (environment) · watchguard-firebox-t20 (environment) · watchguard-firebox-t25 (environment) · watchguard-firebox-t40 (environment) · watchguard-firebox-t45 (environment) · watchguard-firebox-t55 (environment) · watchguard-firebox-t70 (environment) · watchguard-firebox-t80 (environment) · watchguard-firebox-t85 (environment) · watchguard-fireboxv (environment)

Firebox Cloud · WatchGuarddevice

80%

All versions

Firebox M270 · WatchGuarddevice

80%

All versions

Firebox M290 · WatchGuarddevice

80%

All versions

Firebox M295 · WatchGuarddevice

80%

All versions