CVE-2026-3987: WatchGuard Firebox Arbitrary File Write vis Path Traversal in Fireware Web UI

Severity: high (CVSS 7.2 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-01 · updated 2026-10-26
Weakness: CWE-22

Description

A path traversal vulnerability in the Fireware OS Web UI on WatchGuard Firebox systems may allow a privileged authenticated remote attacker to execute arbitrary code in the context of an elevated system process.

Affected products

WatchGuard Fireware OS: from 2025.1 before 2026.2; from 12.6.1 before 12.12 — fixed in 2026.2, 12.12

How to fix

Upgrade to a fixed version: WatchGuard Fireware OS 2026.2, 12.12. Check the vendor advisory for mitigations.

References

https://psirt.watchguard.com/CVE-2026-3987
https://www.watchguard.com/wgrd-psirt/advisory/wgsa-2026-00009

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