CVE-2026-13375: WatchGuard Fireware OS XSS Vulnerability

CVE-2026-13375 Overview

CVE-2026-13375 is a stored Cross-Site Scripting (XSS) vulnerability in the Autotask Technology Integration module of WatchGuard Fireware OS. The flaw stems from improper neutralization of input during web page generation [CWE-79]. WatchGuard identifies this issue as an additional unmitigated attack path for the previously disclosed CVE-2025-13938. Authenticated administrators with high privileges can inject persistent script payloads that execute in the browsers of other management users. Affected releases span Fireware OS 12.4 through 12.12, 12.5 through 12.5.18, and 2025.1 through 2026.2, covering the full Firebox appliance lineup including M-series, T-series, NV5, FireboxV, and FireboxCloud.

Critical Impact
Stored script payloads persist in the Fireware management interface and execute in other administrator sessions, enabling limited confidentiality and integrity impact on subsequent components.

Affected Products

WatchGuard Fireware OS 12.4 up to and including 12.12
WatchGuard Fireware OS 12.5 up to and including 12.5.18
WatchGuard Fireware OS 2025.1 up to and including 2026.2 (Firebox M, T, NV5, FireboxV, FireboxCloud appliances)

Discovery Timeline

2026-07-03 - CVE-2026-13375 published to NVD
2026-07-09 - Last updated in NVD database

Technical Details for CVE-2026-13375

Vulnerability Analysis

The vulnerability resides in the Autotask Technology Integration module of Fireware OS. This module handles integration data between the Firebox appliance and Autotask professional services automation workflows. Input processed by the module is rendered back into the web management interface without adequate output encoding or sanitization.

An attacker who has already obtained high-privilege administrative access to Fireware can submit crafted values that are stored server-side. When another management user loads the affected page, the injected script executes in their browser session under the origin of the Fireware management UI. WatchGuard explicitly describes this issue as a bypass path that was not addressed by the fix for CVE-2025-13938, meaning environments patched only against the earlier CVE remain exposed.

Root Cause

The root cause is missing or insufficient contextual output encoding when rendering Autotask integration fields into HTML responses. Fireware stores attacker-supplied data and later emits it into the Document Object Model (DOM) without escaping HTML control characters such as <, >, and ". This allows script tags or event handlers to be interpreted by the browser rather than displayed as text.

Attack Vector

Exploitation requires network access to the Fireware management interface plus valid high-privilege credentials. The attacker configures the Autotask integration with a payload containing script content. User interaction is required — another operator must view the affected management view for the payload to fire. Successful exploitation can be used to alter management UI content, exfiltrate session-scoped data, or pivot administrative actions within the browser context. No verified public proof-of-concept has been released.

Detection Methods for CVE-2026-13375

Indicators of Compromise

Unexpected HTML tags, <script> fragments, or JavaScript event handlers (onerror=, onload=) stored in Autotask integration configuration fields.
Fireware audit log entries showing configuration changes to the Autotask Technology Integration module from unusual source IPs or outside change-window hours.
Management UI sessions exhibiting outbound requests to unfamiliar domains shortly after loading Autotask-related pages.

Detection Strategies

Review current Autotask integration settings on all Firebox appliances and compare stored field values against a known-good baseline.
Inspect Fireware configuration exports for HTML metacharacters in fields that should contain only alphanumeric identifiers, URLs, or API tokens.
Correlate administrator authentication events with subsequent Autotask configuration writes to identify anomalous privileged activity.

Monitoring Recommendations

Forward Fireware system and audit logs to a centralized logging or SIEM platform and alert on modifications to Autotask integration settings.
Monitor management interface access for unexpected source addresses, especially any exposure of the Fireware web UI to untrusted networks.
Track browser-side anomalies from administrator workstations, including unexpected script execution or DOM-based requests originating from the Firebox management origin.

How to Mitigate CVE-2026-13375

Immediate Actions Required

Apply the fixed Fireware OS release referenced in the WatchGuard Security Advisory WGSA-2026-00017 as soon as it is available for your platform.
Restrict Fireware management interface access to trusted administrative networks and disable exposure to the public internet.
Audit and clear any suspicious content stored in Autotask Technology Integration fields before patching to avoid re-triggering the payload after upgrade.
Rotate administrator credentials and review privileged account membership, since exploitation requires high privileges.

Patch Information

WatchGuard has published guidance under advisory WGSA-2026-00017. Administrators should upgrade to the Fireware OS build identified in that advisory for their branch (12.x or 2025.1+). Refer to the WatchGuard Security Advisory for the authoritative list of fixed versions and upgrade instructions. Environments that only applied the fix for CVE-2025-13938 must still install this update because CVE-2026-13375 represents an unmitigated attack path.

Workarounds

Limit Autotask Technology Integration configuration permissions to a minimal set of trusted administrators.
Enforce multi-factor authentication for all Fireware administrative accounts to reduce risk of credential compromise leading to exploitation.
Access the Fireware web management UI only from dedicated administrative workstations with strict browser hardening and no general web browsing.