How severe is CVE-2026-4266?

CVE-2026-4266 has a CVSS 3.x base score of 6.7, rated medium severity. It is exploitable over local access with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-4266 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (19th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-4266?

CVE-2026-4266 affects Watchguard Fireware. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-4266?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-4266 have an EU (EUVD) identifier?

Yes. CVE-2026-4266 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-17079.

When was CVE-2026-4266 published?

CVE-2026-4266 was published on 2026-03-30 and last updated on 2026-08-14.

CVE-2026-4266

CVE-2026-4266 is a medium-severity vulnerability in Watchguard Fireware with a CVSS 3.x base score of 6.7. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-502.

Key facts

Severity: Medium (CVSS 3.x base score 6.7)
CVSS v4: 8.4
EPSS exploit prediction: 0% (19th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-17079
Weakness: CWE-502
Affected product: Watchguard Fireware
Published: 2026-03-30
Last modified: 2026-08-14

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-4266?: CVE-2026-4266 has a CVSS 3.x base score of 6.7, rated medium severity. It is exploitable over local access with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-4266 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (19th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-4266?: CVE-2026-4266 affects Watchguard Fireware. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-4266?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-4266 have an EU (EUVD) identifier?: Yes. CVE-2026-4266 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-17079.
When was CVE-2026-4266 published?: CVE-2026-4266 was published on 2026-03-30 and last updated on 2026-08-14.

References

Affected products (1)

cpe:2.3:o:watchguard:fireware:*:*:*:*:*:*:*:*

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