CVE-2026-8247: WatchGuard Fireware OS RCE Vulnerability

CVE-2026-8247 Overview

CVE-2026-8247 is an out-of-bounds write vulnerability in WatchGuard Fireware OS that allows an unauthenticated attacker on the same local network segment to execute arbitrary code. The flaw is classified under CWE-120 (Buffer Copy without Checking Size of Input). Fireware OS versions 11.0 through 11.12.4_Update1, 12.0 through 12.12, and 2025.1 through 2026.2 are affected. WatchGuard published details in the WatchGuard Security Advisory.

Critical Impact
An adjacent network attacker without credentials can achieve arbitrary code execution on affected WatchGuard firewalls, compromising perimeter defenses that segment protected networks.

Affected Products

WatchGuard Fireware OS 11.0 through 11.12.4_Update1
WatchGuard Fireware OS 12.0 through 12.12
WatchGuard Fireware OS 2025.1 through 2026.2

Discovery Timeline

2026-07-03 - CVE-2026-8247 published to NVD
2026-07-07 - Last updated in NVD database

Technical Details for CVE-2026-8247

Vulnerability Analysis

CVE-2026-8247 stems from an out-of-bounds write condition in the Fireware OS network stack. The vulnerability arises when the firewall processes attacker-controlled input from the local network segment without adequate bounds checking. Writing beyond the intended buffer corrupts adjacent memory regions, which an attacker can leverage to redirect execution flow.

The issue maps to CWE-120, classic buffer copy without input size validation. Because the attack occurs at the adjacent network layer, exploitation does not require routing through additional infrastructure. An attacker on the same broadcast domain, VLAN, or directly connected segment can deliver the malicious payload. Successful exploitation grants control over a device that enforces network segmentation, inspects traffic, and terminates VPN tunnels.

Root Cause

The root cause is missing or insufficient boundary validation when Fireware OS copies attacker-supplied data into a fixed-size buffer. The processing routine trusts the length or structure of incoming network data, allowing writes past the allocated region. This corrupts control structures such as return addresses, function pointers, or heap metadata used by the firewall firmware.

Attack Vector

The attack vector is Adjacent Network. The attacker must be positioned on the same local network segment as a vulnerable Fireware OS appliance. No authentication and no user interaction are required. Confidentiality, integrity, and availability of the affected device are all impacted. An EPSS score of 0.201% reflects a low observed likelihood of exploitation activity in the short term, but the technical impact of a compromised firewall is severe. Refer to the WatchGuard Security Advisory for vendor technical details.

Detection Methods for CVE-2026-8247

Indicators of Compromise

Unexpected reboots, crashes, or diagnostic log gaps on WatchGuard Firebox appliances running vulnerable Fireware OS versions.
Outbound connections from the firewall management plane to unknown external hosts.
New or modified administrative accounts, policies, or VPN configurations without a corresponding change ticket.
Anomalous ARP, broadcast, or multicast traffic targeting the firewall management interface from adjacent hosts.

Detection Strategies

Monitor Fireware OS system logs for kernel panics, watchdog resets, or process termination events tied to network handlers.
Baseline management-plane traffic and alert on protocol anomalies originating from the local segment.
Correlate switch port and MAC address telemetry to identify unauthorized devices sharing broadcast domains with firewalls.

Monitoring Recommendations

Forward Fireware OS syslog to a centralized SIEM and retain configuration change events for post-incident review.
Enable integrity monitoring for firewall configuration exports and firmware version strings.
Track NetFlow or IPFIX from firewalls to detect lateral movement or command-and-control activity sourced from the appliance itself.

How to Mitigate CVE-2026-8247

Immediate Actions Required

Inventory all WatchGuard Firebox devices and identify appliances running Fireware OS versions in the affected ranges.
Apply the fixed Fireware OS release referenced in the WatchGuard Security Advisory as soon as a maintenance window permits.
Restrict physical and logical access to network segments adjacent to firewall interfaces until patches are deployed.
Rotate administrative credentials and API keys on any appliance suspected of exposure.

Patch Information

WatchGuard has published remediation guidance in advisory wgsa-2026-00026. Administrators should upgrade Fireware OS to the fixed version identified in the advisory for their branch (11.x, 12.x, or 2025.x/2026.x). Verify the running version with show version or the Web UI status page after upgrade.

Workarounds

Enforce strict Layer 2 segmentation and disable unused switch ports adjacent to firewall interfaces to limit reachability.
Apply 802.1X or MAC-based port authentication on switches serving firewall-connected segments.
Place management interfaces on dedicated, isolated VLANs with access limited to authorized administrator hosts.

bash

# Verify Fireware OS version after upgrade
ssh admin@<firebox-ip>
show sysinfo | include Firmware