CVE-2026-34815: Endian Firewall Stored XSS Vulnerability

CVE-2026-34815 Overview

Endian Firewall version 3.3.25 and prior versions are vulnerable to a stored cross-site scripting (XSS) vulnerability via the DOMAIN parameter to /cgi-bin/smtpdomains.cgi. An authenticated attacker can inject arbitrary JavaScript code that is persistently stored on the server and executed when other users view the affected page. This vulnerability type (CWE-79) allows attackers to execute malicious scripts in the context of other users' browser sessions.

Critical Impact

Authenticated attackers can inject persistent malicious JavaScript code that executes in the browsers of other users accessing the SMTP domains configuration page, potentially leading to session hijacking, credential theft, or administrative actions performed on behalf of victims.

Affected Products

• Endian Firewall version 3.3.25
• Endian Firewall versions prior to 3.3.25

Discovery Timeline

• 2026-04-02 - CVE CVE-2026-34815 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-34815

Vulnerability Analysis

This stored cross-site scripting (XSS) vulnerability exists in the Endian Firewall's SMTP domain management functionality. The web application fails to properly sanitize user-supplied input in the DOMAIN parameter before storing it in the backend and subsequently rendering it back to users. When an authenticated user submits a malicious payload through this parameter, the payload is stored in the application's data store. Subsequently, when any user navigates to the page displaying SMTP domain configurations, the stored malicious script is retrieved and executed within their browser context.

The vulnerability requires authentication to exploit, meaning an attacker must first obtain valid credentials to the Endian Firewall administrative interface. However, once exploited, the injected script executes in the security context of any user viewing the compromised page, including administrators with elevated privileges.

Root Cause

The root cause of this vulnerability is insufficient input validation and output encoding in the /cgi-bin/smtpdomains.cgi CGI script. The application does not properly sanitize or encode the DOMAIN parameter value before storing it or rendering it in HTML output. This allows attackers to inject HTML and JavaScript code that the browser interprets as legitimate content from the application.

Attack Vector

The attack vector is network-based, requiring the attacker to have authenticated access to the Endian Firewall web management interface. The attacker submits a specially crafted request to the /cgi-bin/smtpdomains.cgi endpoint with malicious JavaScript embedded in the DOMAIN parameter. The payload is stored server-side and executes whenever the affected SMTP domains configuration page is loaded by any authenticated user.

The vulnerability allows execution of arbitrary JavaScript code in victim browsers, which can be used to steal session cookies, perform administrative actions, redirect users to malicious sites, or harvest credentials through fake login forms.

Detection Methods for CVE-2026-34815

Indicators of Compromise

• Unusual or suspicious entries in SMTP domain configuration containing JavaScript or HTML tags
• Web server logs showing requests to /cgi-bin/smtpdomains.cgi with encoded script payloads in the DOMAIN parameter
• Unexpected administrative actions or configuration changes without corresponding administrator activity

Detection Strategies

• Review web application logs for requests to /cgi-bin/smtpdomains.cgi containing suspicious patterns such as <script>, javascript:, or encoded variants
• Implement Web Application Firewall (WAF) rules to detect and block XSS payloads in HTTP parameters
• Audit SMTP domain configuration entries for any containing HTML or JavaScript content

Monitoring Recommendations

• Enable detailed logging for all CGI script access on the Endian Firewall
• Configure alerting for any requests containing potential XSS payloads targeting the firewall management interface
• Monitor for anomalous user session behavior that may indicate session hijacking

How to Mitigate CVE-2026-34815

Immediate Actions Required

• Restrict access to the Endian Firewall administrative interface to trusted networks and administrators only
• Review existing SMTP domain configurations for any suspicious entries containing script tags or JavaScript
• Implement network-level access controls to limit who can access the management interface
• Consider deploying a Web Application Firewall (WAF) in front of the management interface to filter XSS payloads

Patch Information

Consult the Endian Community Help Section for the latest security updates and patches. Additionally, review the VulnCheck Advisory on Endian Firewall for detailed technical information and remediation guidance.

Workarounds

• Limit administrative access to the Endian Firewall management interface to only trusted, internal networks
• Implement additional authentication mechanisms such as VPN requirements for accessing the management interface
• Regularly audit SMTP domain configurations and remove any suspicious or unexpected entries
• Consider implementing Content Security Policy (CSP) headers at the network edge to mitigate script execution

# Example: Restrict access to management interface via iptables
# Allow only trusted management network (adjust IP range as needed)
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP