CVE-2026-13086: WatchGuard Fireware Buffer Overflow Flaw

CVE-2026-13086 Overview

CVE-2026-13086 is a stack-based buffer overflow in the Endpoint Protection Manager (epm) service in WatchGuard Fireware OS. The flaw resides in the deprecated Mobile Security feature and permits an unauthenticated remote attacker to execute arbitrary code on affected appliances. The weakness maps to [CWE-121: Stack-Based Buffer Overflow] and is reachable over the network without user interaction. Successful exploitation grants code execution in the context of the vulnerable service, which typically runs with elevated privileges on the firewall. WatchGuard published advisory details on its PSIRT portal.

Critical Impact
Unauthenticated remote code execution on WatchGuard Fireware OS appliances exposing the deprecated Mobile Security feature, enabling full compromise of perimeter security devices.

Affected Products

WatchGuard Fireware OS versions that include the deprecated Mobile Security feature
WatchGuard Firebox appliances running the epm (Endpoint Protection Manager) service
Deployments where the Mobile Security feature has not been disabled or removed

Discovery Timeline

2026-08-28 - CVE-2026-13086 published to the National Vulnerability Database (NVD)
2026-09-03 - Last updated in NVD database

Technical Details for CVE-2026-13086

Vulnerability Analysis

The vulnerability exists in the epm service that supports the Mobile Security feature in Fireware OS. The service accepts network input and copies attacker-supplied data into a fixed-size stack buffer without correctly validating the input length. An attacker who reaches the listening service can overflow the stack frame, overwrite the saved return address or adjacent control data, and redirect execution to attacker-controlled code. Because the affected feature is exposed to unauthenticated remote clients, no valid credentials or prior access are required. The flaw is classified as [CWE-121], and the current EPSS probability is 0.441%.

Root Cause

The root cause is missing or incorrect bounds checking during the handling of client-supplied data within the epm service. Data written to a stack-allocated buffer exceeds the buffer's declared size, corrupting adjacent stack memory. Because the affected code path is part of a feature marked deprecated by the vendor, it did not receive the same hardening applied to actively maintained Fireware components.

Attack Vector

An attacker sends a crafted request to the network endpoint served by the epm process on an exposed Fireware OS appliance. No authentication or user interaction is required. The overflow allows corruption of stack control data, leading to arbitrary code execution within the service context. Exploitation of a firewall service places the attacker in a position to intercept, modify, or reroute traffic that traverses the appliance.

No public proof-of-concept code has been released. Refer to the WatchGuard CVE-2026-13086 advisory for vendor-supplied technical details.

Detection Methods for CVE-2026-13086

Indicators of Compromise

Unexpected epm process crashes, restarts, or core dumps on Fireware OS appliances
Inbound traffic to Mobile Security service ports from untrusted or unexpected source addresses
New or unexplained outbound connections initiated by the firewall appliance itself
Configuration changes, new administrative accounts, or altered firewall rules made outside change-management windows

Detection Strategies

Inspect Fireware OS logs for repeated epm service faults or abnormal restart cycles that correlate with inbound requests
Alert on network flows targeting Mobile Security service endpoints from sources outside administrative networks
Compare running configuration against known-good baselines to identify unauthorized modifications
Monitor for anomalous shell activity, process spawning, or filesystem changes on the appliance where telemetry is available

Monitoring Recommendations

Forward Fireware OS syslog to a centralized platform such as an AI SIEM or data lake for retention and correlation
Build alerts that combine service crash events with inbound network requests to the affected feature
Track outbound connections from firewall management interfaces to identify post-exploitation command-and-control activity

How to Mitigate CVE-2026-13086

Immediate Actions Required

Apply the fixed Fireware OS release identified in the WatchGuard PSIRT advisory as soon as it is available for your platform
Disable the deprecated Mobile Security feature on all Firebox appliances that do not require it
Restrict network access to the epm service to trusted management networks using firewall policy
Audit administrative accounts, VPN configurations, and firewall rules for unauthorized changes

Patch Information

WatchGuard has published guidance for CVE-2026-13086 through its Product Security Incident Response Team. Administrators should consult the WatchGuard CVE-2026-13086 advisory for the list of affected Fireware OS versions and the corresponding fixed builds. Because the affected feature is deprecated, vendor guidance may recommend disabling Mobile Security in addition to, or instead of, upgrading.

Workarounds

Disable the Mobile Security feature entirely on appliances where it is not in active use
Block external access to the ports used by the epm service at upstream network devices
Place management and Mobile Security services behind a jump host or VPN reachable only from administrative networks
Enable enhanced logging on affected appliances to accelerate identification of exploitation attempts

bash

# Configuration example: restrict access to the epm service to a management subnet
# Replace 10.0.0.0/24 with your administrative network range
# Apply via Fireware Policy Manager or the Web UI, not directly on the device shell
policy add name="Restrict-EPM" \
  from=any-external \
  to=firebox \
  service=epm \
  action=deny

policy add name="Allow-EPM-Mgmt" \
  from=10.0.0.0/24 \
  to=firebox \
  service=epm \
  action=allow