CVE-2026-86104: Fireware OS Login Process DoS Vulnerability

CVE-2026-86104 Overview

CVE-2026-86104 is an uncontrolled resource consumption vulnerability [CWE-400] in the WatchGuard Fireware OS login process (wgagent). A remote, unauthenticated attacker can trigger a denial of service (DoS) by sending a specially crafted request to the affected component. The flaw affects the availability of the firewall appliance without requiring authentication or user interaction.

Critical Impact
Unauthenticated network attackers can exhaust resources in the wgagent login process, disrupting management access and network protection functions delivered by Fireware OS.

Affected Products

WatchGuard Fireware OS (see the WatchGuard CVE-2026-86104 Advisory for exact affected versions)
The wgagent login component of Fireware OS
WatchGuard Firebox appliances running vulnerable Fireware OS builds

Discovery Timeline

2026-09-30 - CVE-2026-86104 published to NVD
2026-09-30 - Last updated in NVD database

Technical Details for CVE-2026-86104

Vulnerability Analysis

The vulnerability resides in wgagent, the process that handles authentication requests on Fireware OS. A specially crafted request received during the login flow causes the process to consume system resources without proper bounds. Because wgagent is exposed to unauthenticated network clients, an attacker only needs network reachability to the management interface or exposed login service.

Sustained exploitation degrades the availability of the firewall. Loss of the login service can prevent administrators from managing the device and disrupt authentication-dependent functions. The issue is classified as CWE-400 (Uncontrolled Resource Consumption), indicating the code fails to enforce limits on resources consumed while processing attacker-controlled input.

Root Cause

The root cause is missing or insufficient validation of request parameters and resource limits in the wgagent login handler. The process allocates or holds resources based on attacker-supplied input without applying quotas, timeouts, or bounds checks that would otherwise prevent exhaustion.

Attack Vector

The attack vector is network-based and pre-authentication. An attacker sends a crafted login request to the Fireware OS management or authentication endpoint. Repeated or amplified requests exhaust CPU, memory, or connection resources tied to wgagent, resulting in denial of service. No credentials, user interaction, or elevated privileges are required.

No public proof-of-concept or exploit code is currently available in ExploitDB or the CISA Known Exploited Vulnerabilities catalog. Refer to the WatchGuard CVE-2026-86104 Advisory for vendor-supplied technical detail.

Detection Methods for CVE-2026-86104

Indicators of Compromise

Unexpected crashes, restarts, or unresponsiveness of the wgagent process on Fireware OS devices
Spikes in CPU or memory utilization on Firebox appliances that correlate with inbound login traffic
High volumes of malformed or repetitive authentication requests reaching the firewall management interface
Administrators unable to reach the Fireware OS management console during traffic spikes

Detection Strategies

Monitor Fireware OS system logs for wgagent errors, aborts, or resource-allocation failures
Alert on abnormal rates of pre-authentication requests to the Firebox management or authentication service
Correlate management-plane availability loss with concurrent inbound network activity on login ports

Monitoring Recommendations

Ingest Firebox syslog and SNMP counters into a central SIEM for baselining and anomaly detection
Track connection counts and process resource metrics for wgagent over time
Configure alerts for management interface unreachability that coincides with external scanning or flooding activity

How to Mitigate CVE-2026-86104

Immediate Actions Required

Apply the security update referenced in the WatchGuard CVE-2026-86104 Advisory as soon as it is available for your Fireware OS version
Restrict access to the Fireware OS management interface to trusted administrative networks only
Review firewall rules to ensure authentication endpoints are not exposed to the public internet unnecessarily
Enable rate limiting or geo-based filtering in front of the management interface where supported

Patch Information

WatchGuard has published guidance and fixed builds in the WatchGuard CVE-2026-86104 Advisory. Administrators should consult the advisory for the specific fixed Fireware OS versions applicable to their Firebox model and upgrade path.

Workarounds

Limit inbound access to the Fireware OS login service using policy-based source IP restrictions
Place the management interface behind a VPN or bastion host to eliminate direct internet exposure
Deploy upstream rate limiting on TCP connections destined for the Firebox authentication ports
Monitor and terminate anomalous authentication sessions until patched builds are deployed

bash

# Configuration example: restrict Fireware management access to a trusted admin subnet
# (Illustrative - apply equivalent policy in WatchGuard Policy Manager or Web UI)
allow from 10.10.0.0/24 to firebox any-management-port
deny  from any        to firebox any-management-port