CVE-2026-34806: Endian Firewall Stored XSS Vulnerability

CVE-2026-34806 Overview

CVE-2026-34806 is a stored cross-site scripting (XSS) vulnerability affecting Endian Firewall version 3.3.25 and prior. The flaw exists in the /cgi-bin/snat.cgi endpoint, where the remark parameter fails to properly sanitize user input before storing it. An authenticated attacker can inject arbitrary JavaScript code that persists in the system and executes when other users view the affected page, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of legitimate administrators.

Critical Impact

Authenticated attackers can inject persistent malicious JavaScript that executes in the security context of other users viewing SNAT configuration pages, enabling session theft and administrative account compromise on network firewall infrastructure.

Affected Products

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

Discovery Timeline

• 2026-04-02 - CVE-2026-34806 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-34806

Vulnerability Analysis

This stored XSS vulnerability (CWE-79) occurs due to insufficient input validation and output encoding in the Endian Firewall web interface. The remark parameter in the /cgi-bin/snat.cgi CGI script accepts user-controlled input that is stored in the system configuration without proper sanitization. When other authenticated users access pages that display SNAT rules with the malicious remark content, the injected JavaScript executes within their browser session.

The network-based attack vector requires low privileges (authenticated access) and depends on user interaction—specifically, another user must view the page containing the stored payload. While the direct technical impact on the vulnerable system itself is limited, the cross-site nature of this vulnerability means successful exploitation affects the security of the user's session and any subsequent systems they can access through the compromised administrative interface.

Root Cause

The root cause is improper input validation and insufficient output encoding in the Endian Firewall CGI script handling SNAT rule configuration. The remark parameter is written directly to configuration storage and later rendered in HTML output without appropriate escaping, allowing script tags and JavaScript event handlers to be preserved and executed in the browser context of viewing users.

Attack Vector

Exploitation requires an authenticated attacker with access to the Endian Firewall web administration interface. The attacker crafts a malicious SNAT rule containing JavaScript in the remark field. When this configuration is saved, the payload is stored persistently. Subsequently, when any administrator or privileged user views the SNAT configuration page, the stored script executes in their browser session.

The attack enables session cookie theft, keylogging of administrative credentials, modification of firewall rules through the victim's session, or redirection to phishing pages. Since Endian Firewall is network security infrastructure, compromise of an administrator session could lead to broader network security degradation.

Detection Methods for CVE-2026-34806

Indicators of Compromise

• Presence of JavaScript tags, event handlers, or encoded script content in SNAT rule remark fields
• Unusual or unexpected entries in /cgi-bin/snat.cgi access logs with suspicious parameter values
• Administrative session tokens being transmitted to external domains
• Unexpected configuration changes in SNAT rules that were not authorized

Detection Strategies

• Review SNAT rule configurations for suspicious content in remark fields containing <script>, javascript:, onerror=, onload=, or similar patterns
• Monitor web server logs for POST requests to /cgi-bin/snat.cgi with encoded special characters in the remark parameter
• Implement Content Security Policy (CSP) headers to detect and block inline script execution attempts
• Enable browser-based XSS auditors and logging where available

Monitoring Recommendations

• Configure log aggregation for Endian Firewall CGI access logs with alerting on suspicious parameter patterns
• Monitor for outbound connections from administrator workstations to unknown external domains following firewall administration sessions
• Track configuration changes to SNAT rules with alerting on remark field modifications

How to Mitigate CVE-2026-34806

Immediate Actions Required

• Audit all existing SNAT rules for suspicious JavaScript content in remark fields and remove any malicious entries
• Restrict access to the Endian Firewall web administration interface to trusted networks only
• Implement network segmentation to limit who can access the firewall management interface
• Consider deploying a web application firewall (WAF) in front of the management interface to filter XSS payloads

Patch Information

Monitor the Endian Community Support portal for security updates addressing this vulnerability. Review the VulnCheck Security Advisory for additional technical details and remediation guidance.

Workarounds

• Restrict administrative access to the Endian Firewall web interface to a limited set of trusted IP addresses
• Use browser extensions or settings that block inline JavaScript execution when accessing the firewall management interface
• Implement strict Content Security Policy headers at the reverse proxy level if the firewall is accessed through one
• Regularly audit SNAT rule remarks for suspicious content as part of routine security hygiene

# Example: Restrict management interface access via iptables
# Allow management access only from trusted admin network
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP