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FirewareOperating system · Watchguard

CVE-2026-4266

MEDIUM · 6.7 CVSS v3.1 Published 2026-03-30
Fix available
A fix is available. Upgrade to 12.12 / 2026.2 or later.
See remediation →
69/100
Remediation priority · Elevated
Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Insecure Deserialization vulnerability in WatchGuard Fireware OS allows an attacker with prior filesystem write access (obtained through a separate vulnerability) to execute arbitrary code in the context of the portald user. The vulnerability affects Access Portal-enabled platforms running versions 12.1-12.11.8 and 2025.1-2026.1.2.

MitigationUpgrade Fireware OS to a patched version beyond 12.11.8 or 2026.1.2. Platforms without Access Portal (T-15, T-35) are not affected. Organizations should also identify and remediate the initial vulnerability that provides filesystem write access, as this is a chained exploitation scenario.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FirewareOperating system
Affected:>= 2025.1, < 2026.2>= 12.1, < 12.12

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
High
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify your WatchGuard platform model
    Determine the specific model number of your WatchGuard Firebox or XTM device. Consult your device documentation or check the physical device label.
    Affected if The device is NOT one of the following Access Portal-disabled models: T-15 or T-35. If your model is different, it may support Access Portal and could be affected.
  2. Check the installed Fireware OS version
    Access the Firebox Web UI or use the CLI command 'fireware -v' or 'system status' to retrieve the current OS version. Note the full version number (e.g., 12.11.3 or 2025.3).
    Affected if The installed version falls within 12.1 through 12.11.8, OR within 2025.1 through 2026.1.2. Versions outside these ranges are not affected.
  3. Verify if Access Portal is enabled
    Log into the Firebox Web UI, navigate to Subscription Services > Access Portal, or use the CLI command 'ap show' to check the Access Portal service status.
    Affected if Access Portal is enabled and running. If it is disabled or not configured, the device is not vulnerable to this issue.
  4. Confirm the portald service is active
    Use the CLI command 'diag debug top' or 'ps aux | grep portald' to verify the portald daemon is running on the device.
    Affected if The portald service is present and running. This is the service in whose context arbitrary code would execute if the chained attack succeeds.

Your device is affected if it is NOT a T-15 or T-35 model, runs Fireware OS within versions 12.1-12.11.8 or 2025.1-2026.1.2, and has Access Portal enabled with the portald service active.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 12.12 / 2026.2 or later
Fixed in 12.122026.2
Interim mitigation

Upgrade Fireware OS to a patched version beyond 12.11.8 or 2026.1.2. Platforms without Access Portal (T-15, T-35) are not affected. Organizations should also identify and remediate the initial vulnerability that provides filesystem write access, as this is a chained exploitation scenario.

Recommended fix Moderate confidence

Upgrade to Fireware OS 12.11.9 or later (for 12.x branch) or 2026.2 or later (for 2025/2026 branch)

  1. 1. Identify the current Fireware OS version installed on the WatchGuard device
  2. 2. Determine if the device supports the Access Portal feature (not affected on T-15 and T-35 models)
  3. 3. For versions 12.1 through 12.11.8: Upgrade to version 12.11.9 or later
  4. 4. For versions 2025.1 through 2026.1.2: Upgrade to version 2026.2 or later
  5. 5. Download the firmware from the official WatchGuard support portal at www.watchguard.com
  6. 6. Upload and apply the firmware upgrade following WatchGuard's standard upgrade procedures
  7. 7. Verify the upgrade was successful and the Access Portal service is functioning correctly
  8. 8. Ensure the system is protected from the initial attack vector that provides filesystem write access
Caveat Review WatchGuard release notes for any configuration changes required after upgrading; ensure backup of configuration before upgrade

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Fireware Scoped from the published advisory
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing8.0 h
  • Review / QA4.0 h
30.0 hours of engineering $5,280
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-4266 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data