What is CVE-2026-4266?

CVE-2026-4266 is a medium-severity vulnerability in Watchguard Firebox Cloud, classified under Deserialization of Untrusted Data. CVSS score: 6.7/10. Published 2026-03-30.

How severe is CVE-2026-4266?

Medium severity. CVSS v3 base score is 6.7 out of 10.

Deserialization in Watchguard Firebox Cloud

CVE-2026-4266

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.

Vulnerability class: Insecure Deserialization

EPSS: 0.003 (20.9th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.7 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H.

Affected products

Weakness classification (CWE)

CWE-502 — Deserialization of Untrusted Data

References

5d1c2695-1a31-4499-88ae-e847036fd7e3 (vendor-advisory, Vendor Advisory)
5d1c2695-1a31-4499-88ae-e847036fd7e3 (vendor-advisory, Broken Link)

Frequently asked questions

What is CVE-2026-4266?: CVE-2026-4266 is a medium-severity vulnerability in Watchguard Firebox Cloud, classified under Deserialization of Untrusted Data. CVSS score: 6.7/10. Published 2026-03-30.
How severe is CVE-2026-4266?: Medium severity. CVSS v3 base score is 6.7 out of 10.