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Fireware OS CVE-2026-13377

| EUVDEUVD-2026-41452 MEDIUM
Cross-site Scripting (XSS) (CWE-79)
2026-07-02 WatchGuard GHSA-8pfv-rw6v-3qpv
XSS Watchguard Fireware Os
4.8
CVSS 4.0 · Vendor: WatchGuard
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Severity by source

Vendor (WatchGuard) PRIMARY
4.8 MEDIUM
CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
4.8 MEDIUM

High privileges required to inject stored payload; scope change to victim browser; low confidentiality and integrity impact via session hijack or UI manipulation with no availability impact.

3.1 AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N
4.0 AV:N/AC:L/AT:N/PR:H/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

Primary rating from Vendor (WatchGuard).

CVSS VectorVendor: WatchGuard

CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector
Network
Attack Complexity
Low
Privileges Required
High
User Interaction
P
Scope
X

Lifecycle Timeline

1
Analysis Generated
Jul 02, 2026 - 23:56 vuln.today

DescriptionCVE.org

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.

This issue affects Fireware OS 12.0 up to and including 12.12, 12.5 up to and including 12.5.18, and 2025.1 up to and including 2026.2.

AnalysisAI

Stored XSS in WatchGuard Fireware OS's SIP Proxy module enables a high-privileged attacker to plant persistent malicious JavaScript that executes in the browsers of other privileged users who access affected management interface pages. Covering Fireware OS versions 12.0 through 12.12, 12.5 through 12.5.18, and 2025.1 through 2026.2, this CVE is explicitly disclosed as an additional, previously unmitigated attack path for CVE-2025-6947 - meaning organizations that applied the prior patch may incorrectly believe their exposure is closed. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Obtain high-privileged admin credentials
Delivery
Access SIP Proxy module in management UI
Exploit
Inject persistent JavaScript payload into module data field
Execution
Victim admin navigates to affected management page
Persist
Browser executes attacker's stored script
Impact
Exfiltrate session tokens or credentials
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Vulnerability AssessmentAI

Exploitation The attacker must hold a high-privileged account (PR:H) on the WatchGuard Fireware OS management interface - standard read-only or operator-level accounts are insufficient to inject into the SIP Proxy module. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 4.0 score of 4.8 (Medium) accurately reflects the constrained real-world risk. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker who has obtained or holds a high-privileged WatchGuard administrator account injects a crafted JavaScript payload into a SIP Proxy module configuration field or data display surface that is subsequently stored and rendered in the Fireware OS management interface. When a second administrator authenticates and navigates to the affected management page, their browser silently executes the stored script, potentially exfiltrating session tokens, authentication cookies, or management credentials to an attacker-controlled endpoint. …
Remediation Consult the WatchGuard advisory WGSA-2026-00019 at https://www.watchguard.com/wgrd-psirt/advisory/wgsa-2026-00019 for the upgrade path; exact patched version numbers are not independently confirmed from available input data and must be sourced directly from the advisory. … Detailed patch versions, workarounds, and compensating controls in full report.
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Threat intelligence, references, and detailed analysis are available after sign-in.

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CVE-2026-13377 vulnerability details – vuln.today
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