CVE-2026-4266
WatchGuard Firebox Insecure Deserialization in Fireware Access Portal
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.
INFO
Published Date :
March 30, 2026, 1:16 p.m.
Last Modified :
Aug. 14, 2026, 1:38 p.m.
Remotely Exploit :
No
Source :
5d1c2695-1a31-4499-88ae-e847036fd7e3
Affected Products
The following products are affected by CVE-2026-4266
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 4.0 | HIGH | 5d1c2695-1a31-4499-88ae-e847036fd7e3 | ||||
| CVSS 4.0 | HIGH | 5d1c2695-1a31-4499-88ae-e847036fd7e3 |
Solution
- Update WatchGuard Fireware OS to a fixed version.
- Apply the latest vendor patches.
- Restrict filesystem write access.
- Disable Access Portal if unused.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-4266.
| URL | Resource |
|---|---|
| https://psirt.watchguard.com/CVE-2026-4266 | Broken Link |
| https://www.watchguard.com/wgrd-psirt/advisory/wgsa-2026-00007 | Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-4266 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-4266
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-4266 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-4266 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Aug. 14, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H Added CPE Configuration AND OR *cpe:2.3:o:watchguard:fireware:*:*:*:*:*:*:*:* versions from (including) 2025.1 up to (excluding) 2026.2 OR cpe:2.3:h:watchguard:firebox_t115-w:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_t125:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_t125-w:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_t145:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_t145-w:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_t185:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m295:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m395:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m495:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m595:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m695:-:*:*:*:*:*:*:* Added CPE Configuration AND OR *cpe:2.3:o:watchguard:fireware:*:*:*:*:*:*:*:* versions from (including) 12.1 up to (excluding) 12.12 OR cpe:2.3:h:watchguard:firebox_t55:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_t70:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_t20:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_t40:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_t80:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m440:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m270:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m370:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m470:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m570:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m670:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m290:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m390:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m590:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m690:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m4800:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m5800:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:fireboxv:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m4600:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_m5600:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_nv5:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_t25:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_t45:-:*:*:*:*:*:*:* cpe:2.3:h:watchguard:firebox_t85:-:*:*:*:*:*:*:* cpe:2.3:a:watchguard:firebox_cloud:-:*:*:*:*:*:*:* Added Reference Type WatchGuard Technologies, Inc.: https://psirt.watchguard.com/CVE-2026-4266 Types: Broken Link Added Reference Type WatchGuard Technologies, Inc.: https://www.watchguard.com/wgrd-psirt/advisory/wgsa-2026-00007 Types: Vendor Advisory -
CVE Modified by 5d1c2695-1a31-4499-88ae-e847036fd7e3
Aug. 10, 2026
Action Type Old Value New Value Changed Affected [{'vendor': 'WatchGuard', 'product': 'Fireware OS', 'versions': [{'status': 'affected', 'version': '12.1', 'versionType': 'semver', 'lessThanOrEqual': '12.11.8'}, {'status': 'affected', 'version': '2025.1', 'versionType': 'semver', 'lessThanOrEqual': '2026.1.2'}], 'defaultStatus': 'unaffected'}] [{'vendor': 'WatchGuard', 'product': 'Fireware OS', 'versions': [{'status': 'affected', 'version': '2025.1', 'lessThan': '2026.2', 'versionType': 'custom'}, {'status': 'affected', 'version': '12.1', 'lessThan': '12.12', 'versionType': 'custom'}], 'platforms': ['Default'], 'defaultStatus': 'unaffected'}] Changed 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. 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. Added Reference https://psirt.watchguard.com/CVE-2026-4266 -
CVE Modified by 5d1c2695-1a31-4499-88ae-e847036fd7e3
Jun. 17, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'WatchGuard', 'product': 'Fireware OS', 'versions': [{'status': 'affected', 'version': '12.1', 'versionType': 'semver', 'lessThanOrEqual': '12.11.8'}, {'status': 'affected', 'version': '2025.1', 'versionType': 'semver', 'lessThanOrEqual': '2026.1.2'}], 'defaultStatus': 'unaffected'}] -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 17, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-4266', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-03-30T00:00:00+00:00'} -
New CVE Received by 5d1c2695-1a31-4499-88ae-e847036fd7e3
Mar. 30, 2026
Action Type Old Value New Value Added 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. Added CVSS V4.0 AV:L/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-502 Added Reference https://www.watchguard.com/wgrd-psirt/advisory/wgsa-2026-00007