# CVE-2026-81433 — WatchGuard Fireware OS

> As of 2026-10-01, CVE-2026-81433 is a High-severity (band derived from the CVSS v4.0 score, not stated by the CNA) vulnerability in WatchGuard Fireware OS, CVSS v4.0 8.7, EPSS 0.2% (9.0th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-81433, most recently “WatchGuard Fireware OS Critical Code Injection Vulnerability in BOVPN over TLS Client (CVE-2026-86131)”.

**Last updated:** 2026-10-01

## What is CVE-2026-81433?

A stack-based buffer overflow vulnerability in WatchGuard Fireware OS's DHCP fingerprinting daemon (fingerd) allows an unauthenticated attacker with adjacent network access to execute arbitrary code or crash the process by sending a specially crafted DHCP packet.

The record classifies CVE-2026-81433 under weakness classes [CWE-120](https://intel.threadlinqs.com/cwe/CWE-120), [CWE-121](https://intel.threadlinqs.com/cwe/CWE-121), [CWE-787](https://intel.threadlinqs.com/cwe/CWE-787). 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 25 days ago.

## Severity and exploitation probability

- **CVSS v4.0 base score:** 8.7 — High (derived from score) (`CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **EPSS (FIRST):** 0.2% probability of exploitation in the next 30 days, higher than 9.0% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 4.7/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-09-29, last modified 2026-10-01

## Is CVE-2026-81433 being exploited?

It currently carries a trending score of 35 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [WatchGuard](https://intel.threadlinqs.com/vendors/watchguard): Fireware OS

## How to fix CVE-2026-81433

No vendor patch reference has been recorded for CVE-2026-81433 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-81433

1 tracked threat in the Threadlinqs corpus references CVE-2026-81433, either in the campaign’s CVE list or as an indicator on the campaign record.

- [WatchGuard Fireware OS Critical Code Injection Vulnerability in BOVPN over TLS Client (CVE-2026-86131)](https://intel.threadlinqs.com/threat/TL-2026-2813) — CRITICAL · 2026-09-30

## Sources

Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on 2026-10-10.

**Vendor advisory and patch**

- [psirt.watchguard.com — vendor advisory](https://psirt.watchguard.com/CVE-2026-81433)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-81433
Full detection coverage and IOCs for threats exploiting CVE-2026-81433 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp