WatchGuard Firebox Stored XSS in SIP Proxy (CVE-2026-13377) Advisory

Vulnerability Overview Vulnerability Name: Stored Cross-Site Scripting (XSS) Vulnerability in SIP Proxy Configuration in WatchGuard Firebox CVE Number: CVE-2026-13377 CVSS Score: 4.8 Status: Resolved Publication Date: 2026-07-02 Update Date: 2026-07-02 Summary: A stored cross-site scripting (XSS) vulnerability exists in the input generation of web pages within the SIP proxy module of WatchGuard Firewall OS. This vulnerability is an additional attack path for the unmitigated exploit of CVE-2025-6947. Impact Scope Affected Products: Firebox Affected Versions: - Firebox OS 12.0 to 12.12 - Firebox OS 12.5 to 12.5.18 - Firebox OS 2025.1 to 2026.2 Remediation Resolved Versions: - Firebox OS 2025.1: 2026.2.1 - Firebox OS 12.x: 12.12.1 - Firebox OS 12.5.x (T15 & T35 models): Not Resolved Product List Firebox OS 12.5.x: T15, T35 Firebox OS 2025.1.x: T115-W, T125, T125-W, T145, T145-W, T185, M295, M395, M495, M595, M695 Firebox OS 12.x: T20, T25, T40, T45, T55, T70, T80, T85, M270, M290, M370, M390, M470, M570, M590, M670, M690, M440, M4600, M4800, M5600, M5800, Firebox Cloud, Firebox NV5, FireboxV Additional Information Recommendation: It is recommended to upgrade to the resolved versions as soon as possible to fix the vulnerability. Contact: For more information, please contact the WatchGuard support team.

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WatchGuard Firebox Stored XSS in SIP Proxy (CVE-2026-13377) Advisory