CVE-2026-34805: Endian Firewall Stored XSS Vulnerability

CVE-2026-34805 Overview

CVE-2026-34805 is a stored cross-site scripting (XSS) vulnerability affecting Endian Firewall version 3.3.25 and prior. The vulnerability exists in the remark parameter of the /cgi-bin/dnat.cgi endpoint. An authenticated attacker can inject arbitrary JavaScript code that is stored on the server and subsequently executed in the browsers of other users who view the affected page.

Critical Impact

Authenticated attackers can inject persistent malicious scripts that execute in the context of other users' sessions, potentially leading to session hijacking, credential theft, or unauthorized actions on the firewall management interface.

Affected Products

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

Discovery Timeline

• 2026-04-02 - CVE CVE-2026-34805 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-34805

Vulnerability Analysis

This stored XSS vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation) occurs due to insufficient input sanitization in the Endian Firewall web management interface. When processing the remark parameter submitted to /cgi-bin/dnat.cgi, the application fails to properly validate and encode user-supplied input before storing it in the backend and rendering it in subsequent page views.

The vulnerability is network-accessible and requires low attack complexity, though it does require the attacker to have low-level authenticated access to the firewall management interface. User interaction is required for exploitation, as a victim must view the page containing the injected malicious script.

Root Cause

The root cause is improper input validation and output encoding in the DNAT (Destination Network Address Translation) configuration interface. The remark field, intended to allow administrators to add descriptive notes to NAT rules, does not sanitize special characters such as <, >, ", and '. This allows HTML and JavaScript code to be injected and stored, which is then rendered without proper encoding when the page is displayed to other users.

Attack Vector

The attack is conducted over the network through the web management interface. An authenticated attacker with access to the DNAT configuration page submits a crafted request containing malicious JavaScript in the remark parameter. This payload is stored in the firewall's configuration and executed whenever another authenticated user (including administrators with higher privileges) views the DNAT rules page.

A typical attack scenario involves an attacker with limited administrative access injecting a script that exfiltrates session cookies or performs actions on behalf of a higher-privileged administrator. The stored nature of this XSS makes it particularly dangerous as the payload persists and can affect multiple users over time. For detailed technical information, see the VulnCheck Advisory on Endian Firewall.

Detection Methods for CVE-2026-34805

Indicators of Compromise

• Unusual JavaScript code or HTML tags present in DNAT rule remark fields
• Session cookies being transmitted to external or unexpected domains
• Unexpected administrative actions logged without corresponding administrator activity
• Web server logs showing suspicious encoded payloads in requests to /cgi-bin/dnat.cgi

Detection Strategies

• Monitor HTTP request logs for the remark parameter containing script tags, event handlers (e.g., onerror, onload), or JavaScript URIs
• Implement Content Security Policy (CSP) headers to detect and block inline script execution
• Review DNAT configuration exports for any entries containing HTML or script content
• Deploy web application firewalls (WAF) with rules to detect XSS payloads in form submissions

Monitoring Recommendations

• Enable detailed logging on the Endian Firewall web management interface
• Configure alerts for any modifications to DNAT rules, particularly in the remark fields
• Monitor network traffic for outbound connections from administrator workstations to unknown domains during firewall management sessions
• Implement session anomaly detection to identify potential session hijacking attempts

How to Mitigate CVE-2026-34805

Immediate Actions Required

• Restrict access to the Endian Firewall management interface to trusted networks and IP addresses only
• Review all existing DNAT rule remarks for suspicious content and remove any malicious payloads
• Implement network segmentation to limit who can access the firewall administration interface
• Consider placing a reverse proxy with XSS filtering capabilities in front of the management interface

Patch Information

No official patch information was available at the time of publication. Organizations should monitor the Endian Help Center Community for security updates and upgrade announcements. Apply any security patches as soon as they become available from the vendor.

Workarounds

• Limit authenticated access to the Endian Firewall management interface to only essential personnel
• Use a dedicated, hardened browser session for firewall administration that does not store cookies or credentials
• Implement IP-based access controls to restrict management interface access to specific administrator workstations
• Regularly audit DNAT configurations and sanitize any suspicious remark entries manually
• Consider deploying an additional WAF layer to filter malicious input before it reaches the firewall interface

# Configuration example: Restrict management interface access via iptables
# Add these rules on the Endian Firewall or upstream network device

# Allow management access only from trusted admin subnet
iptables -A INPUT -p tcp --dport 443 -s 10.0.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 10443 -s 10.0.1.0/24 -j ACCEPT

# Drop all other management interface connections
iptables -A INPUT -p tcp --dport 443 -j DROP
iptables -A INPUT -p tcp --dport 10443 -j DROP