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CVE-2026-13377: WatchGuard Firebox Stored Cross-Site-Scripting (XSS) Vulnerability in SIP Proxy Configuration

• Severity: medium (CVSS 4.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-03 · updated 2026-10-25
• Weakness: CWE-79

Description

Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting') vulnerability in WatchGuard Fireware OS SIP Proxy module allows Stored XSS. This vulnerability is an additional unmitigated attack path for CVE-2025-6947.

Affected products

• WatchGuard Fireware OS: from 12.0 before 12.12.1; from 2025.1 before 2026.2.1; from 12.5 through 12.5.18 — fixed in 12.12.1, 2026.2.1

How to fix

Upgrade to a fixed version: WatchGuard Fireware OS 12.12.1, 2026.2.1. Check the vendor advisory for mitigations.

References

• https://psirt.watchguard.com/CVE-2026-13377
• https://www.watchguard.com/wgrd-psirt/advisory/wgsa-2026-00019

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