CVE-2026-34808: Endian Firewall Stored XSS Vulnerability

CVE-2026-34808 Overview

Endian Firewall version 3.3.25 and prior contain a stored cross-site scripting (XSS) vulnerability in the remark parameter of /cgi-bin/outgoingfw.cgi. An authenticated attacker can inject arbitrary JavaScript code that is stored on the server and executed when other users view the affected page. This stored XSS vulnerability (CWE-79) allows attackers to persist malicious scripts within the firewall's web interface, potentially compromising administrator sessions and enabling further attacks against the network infrastructure.

Critical Impact

Authenticated attackers can inject persistent JavaScript payloads into the firewall's outgoing firewall configuration interface, enabling session hijacking, credential theft, and potential administrative takeover of the security appliance.

Affected Products

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

Discovery Timeline

• 2026-04-02 - CVE-2026-34808 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-34808

Vulnerability Analysis

The vulnerability exists in the outgoing firewall rule management interface of Endian Firewall. The remark parameter, which allows administrators to add descriptive notes to firewall rules, fails to properly sanitize user-supplied input before storing it in the application database. When other users (particularly administrators) subsequently view the firewall rules page, the malicious JavaScript payload stored in the remark field is rendered without proper output encoding, causing the script to execute in the context of the victim's browser session.

This stored XSS variant is particularly dangerous in a firewall management context because:

• The firewall interface is typically accessed by privileged users
• Stored payloads persist across sessions and affect multiple victims
• Successful exploitation can lead to session token theft and administrative account compromise

Root Cause

The root cause is improper input validation and output encoding in the /cgi-bin/outgoingfw.cgi endpoint. The application fails to sanitize special characters (such as <, >, ", and ') from the remark parameter before storing the value. Additionally, when displaying the stored remarks, the application does not apply proper HTML entity encoding or context-aware output escaping, allowing injected scripts to execute in victims' browsers.

Attack Vector

The attack requires an authenticated user to submit a malicious payload through the firewall's web interface. The attacker submits a specially crafted JavaScript payload via the remark parameter when creating or modifying an outgoing firewall rule. The payload is stored in the application's data store and executed whenever any user views the firewall rules page.

The attack flow involves an authenticated user accessing the outgoing firewall configuration interface at /cgi-bin/outgoingfw.cgi, injecting a malicious script payload into the remark field (such as a script tag containing JavaScript code to steal cookies or session tokens), and waiting for other administrators to view the firewall rules page where the payload executes in their browser context. This network-based attack requires low privileges (any authenticated user) and user interaction (victim must view the affected page).

Detection Methods for CVE-2026-34808

Indicators of Compromise

• Unusual JavaScript content or HTML tags present in firewall rule remarks
• HTTP requests to /cgi-bin/outgoingfw.cgi containing script tags or event handlers in the remark parameter
• Web access logs showing requests with encoded JavaScript payloads (%3Cscript%3E, javascript:, onerror=, etc.)
• Unexpected outbound connections from administrator workstations after accessing the firewall interface

Detection Strategies

• Implement web application firewall (WAF) rules to detect XSS payloads in HTTP POST requests to /cgi-bin/outgoingfw.cgi
• Monitor firewall configuration changes for the presence of HTML special characters or JavaScript keywords in remark fields
• Deploy browser-based XSS detection using Content Security Policy (CSP) violation reporting
• Analyze HTTP traffic for patterns consistent with stored XSS attacks targeting the firewall management interface

Monitoring Recommendations

• Enable detailed access logging for the Endian Firewall web management interface
• Configure alerting for configuration changes to outgoing firewall rules
• Monitor for CSP violations if Content Security Policy headers are implemented
• Track administrator session activity for anomalous behavior following firewall interface access

How to Mitigate CVE-2026-34808

Immediate Actions Required

• Audit all existing firewall rules for suspicious content in remark fields
• Restrict access to the Endian Firewall web management interface to trusted networks only
• Implement additional authentication controls such as multi-factor authentication for firewall administration
• Consider temporarily disabling the remark functionality if possible until a patch is available

Patch Information

Consult the Endian Community Help Section for the latest security updates and patches. Review the VulnCheck Security Advisory for additional technical guidance and remediation information.

Workarounds

• Restrict web management interface access to specific IP addresses or management VLANs
• Implement a reverse proxy with XSS filtering capabilities in front of the Endian Firewall web interface
• Manually review and sanitize all remark fields in existing firewall rules
• Use browser extensions that block inline script execution when accessing the management interface
• Consider using CLI-based management instead of the web interface until a patch is available

# Example: Restrict access to management interface via iptables
# Only allow management access from trusted admin network
iptables -A INPUT -p tcp --dport 10443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 10443 -j DROP