Medium severity · published Mar 30, 2026
CVE-2026-4266
WatchGuard Firebox Insecure Deserialization in Fireware Access Portal
6.7
CVSS
0.3%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
Attack vector
Local
Complexity
Low
Privileges
High
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 20% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FO
Fireware OS · WatchGuard
2025.1 before 2026.2; 12.1 before 12.12; 12.1 before 12.11.9 · source: vendor
FI
Fireware · Watchguard
2025.1 before 2026.2; 12.1 before 12.12 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-4266
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-4266
Broken Link
https://psirt.watchguard.com/CVE-2026-4266
Vendor Advisory
https://www.watchguard.com/wgrd-psirt/advisory/wgsa-2026-00007
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