8.4

CVE-2026-4266: WatchGuard Firebox Insecure Deserialization in Fireware Access Portal

Analyzed
Published 30-03-2026Last modified 27-08-2026

Vulnerability summary

CVE-2026-4266 is a high (CVSS 8.4) Deserialization of Untrusted Data vulnerability in watchguard fireware. EPSS estimates a 0.39% chance of exploitation in the next 30 days, higher than 31.9% of scored vulnerabilities.

Overall risk
34/100
0100
Medium · default modelHow is this calculated?
CVSS score
8.4/10
010
High · v4.0 (CVE.org)
EPSS score
0.39%
0%100%
Low · +0.12 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Timeline

  1. 30-03-2026
    PublishedVulnerability first disclosed.
  2. 27-08-2026
    Last modifiedVulnerability information updated.

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 metrics

3 scores · 2 sources · 2 versions

EPSS trend

Probability

0.39%

Chance of exploitation in the next 30 days

Percentile

32%

Versus all other CVEs

30-day change

Increase +0.12 pp

From 0.27% on 22-09-2026

22-09-202622-10-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Watchguard2 products
  • fireware≥ 2025.1, < 2026.2 | ≥ 12.1, < 12.12
  • fireware os≥ 2025.1, < 2026.2 | ≥ 12.1, < 12.12 | ≥ 12.1, < 12.11.9

1 vendor · 2 products

References

2 links