CVE-2019-25426: Comodo Dome Firewall XSS Vulnerability

CVE-2019-25426 Overview

Comodo Dome Firewall 2.7.0 contains a reflected cross-site scripting (XSS) vulnerability that allows attackers to inject malicious scripts by submitting crafted input to the dnsmasq endpoint. Attackers can send POST requests with script payloads in the TRANSPARENT_SOURCE_BYPASS or TRANSPARENT_DESTINATION_BYPASS parameters to execute arbitrary JavaScript in users' browsers.

Critical Impact

Attackers can execute arbitrary JavaScript code in the context of authenticated user sessions, potentially leading to session hijacking, credential theft, or unauthorized administrative actions on the firewall management interface.

Affected Products

• Comodo Dome Firewall 2.7.0

Discovery Timeline

• 2026-02-19 - CVE CVE-2019-25426 published to NVD
• 2026-02-19 - Last updated in NVD database

Technical Details for CVE-2019-25426

Vulnerability Analysis

This reflected cross-site scripting vulnerability exists in the dnsmasq endpoint of Comodo Dome Firewall 2.7.0. The web interface fails to properly sanitize user-supplied input before reflecting it back in HTTP responses. When an attacker crafts a malicious POST request containing JavaScript code in specific parameters, the application echoes the payload directly into the response page without proper encoding or escaping.

The vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation), indicating a fundamental input validation failure where user-controllable data is incorporated into web pages without appropriate sanitization measures.

Root Cause

The root cause of this vulnerability is improper input validation and insufficient output encoding in the dnsmasq endpoint handler. The application accepts user input through POST parameters (TRANSPARENT_SOURCE_BYPASS and TRANSPARENT_DESTINATION_BYPASS) and reflects this content back to the browser without sanitizing or encoding special characters that have meaning in HTML/JavaScript contexts. This allows attackers to break out of the expected data context and inject executable script content.

Attack Vector

The attack vector is network-based and requires user interaction to succeed. An attacker must craft a malicious URL or form that submits specially crafted POST data to the vulnerable dnsmasq endpoint. When an authenticated administrator or user with access to the firewall management interface is tricked into clicking the malicious link or submitting the form, the injected JavaScript executes within their browser session.

The exploitation flow involves sending a POST request to the dnsmasq endpoint with malicious JavaScript payloads embedded in the TRANSPARENT_SOURCE_BYPASS or TRANSPARENT_DESTINATION_BYPASS parameters. The server reflects this input without sanitization, causing the victim's browser to execute the attacker-controlled script. Technical details and proof-of-concept code are available in the Exploit-DB #46408 advisory.

Detection Methods for CVE-2019-25426

Indicators of Compromise

• HTTP POST requests to the dnsmasq endpoint containing script tags or JavaScript event handlers in the TRANSPARENT_SOURCE_BYPASS or TRANSPARENT_DESTINATION_BYPASS parameters
• Web server logs showing unusual encoded characters or script patterns in POST body data targeting firewall management endpoints
• Browser console errors or unexpected script execution events on firewall administration pages

Detection Strategies

• Deploy web application firewall (WAF) rules to detect and block common XSS payloads in POST parameters targeting the dnsmasq endpoint
• Implement network-level monitoring for HTTP traffic containing suspicious JavaScript patterns directed at Comodo Dome Firewall management interfaces
• Enable and review access logs for the firewall management interface to identify anomalous request patterns

Monitoring Recommendations

• Monitor authentication logs for successful logins following suspicious XSS-related requests to detect potential session hijacking
• Configure alerting for any access to the dnsmasq endpoint from external or untrusted IP addresses
• Implement browser-based security monitoring to detect unexpected script execution on management interfaces

How to Mitigate CVE-2019-25426

Immediate Actions Required

• Restrict access to the Comodo Dome Firewall management interface to trusted networks and IP addresses only
• Implement network segmentation to isolate firewall management traffic from general user networks
• Deploy a web application firewall with XSS filtering capabilities in front of the management interface
• Educate administrators about the risks of clicking untrusted links while authenticated to the firewall console

Patch Information

Organizations should check the Comodo Firewall product page for the latest firmware updates and security patches. Review the VulnCheck Advisory for Comodo Dome for additional vendor guidance and remediation details.

Workarounds

• Implement strict Content Security Policy (CSP) headers on the firewall management interface to prevent inline script execution
• Configure network access controls to limit management interface access to specific administrator workstations
• Use a reverse proxy with input sanitization capabilities to filter potentially malicious requests before they reach the firewall
• Ensure administrators always access the management interface from a dedicated browser profile without saved sessions to other sites