CVE-2026-34820: Endian Firewall Stored XSS Vulnerability

CVE-2026-34820 Overview

Endian Firewall version 3.3.25 and prior versions contain a stored cross-site scripting (XSS) vulnerability in the IPsec management interface. An authenticated attacker can inject arbitrary JavaScript code via the remark parameter to /manage/ipsec/. The malicious script is stored on the server and executes whenever other users view the affected page, potentially leading to session hijacking, credential theft, or further exploitation of the firewall management interface.

Critical Impact

Authenticated attackers can inject persistent malicious JavaScript into the firewall management interface, potentially compromising administrative sessions and enabling further attacks on the network security infrastructure.

Affected Products

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

Discovery Timeline

• 2026-04-02 - CVE-2026-34820 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-34820

Vulnerability Analysis

This stored cross-site scripting vulnerability exists in the Endian Firewall's IPsec management interface. When an authenticated user submits data through the remark parameter at the /manage/ipsec/ endpoint, the application fails to properly sanitize or encode the input before storing it in the database and subsequently rendering it in the web interface.

Unlike reflected XSS attacks that require victims to click malicious links, stored XSS vulnerabilities persist on the server. In this case, every user who accesses the affected IPsec configuration page will have the malicious JavaScript execute in their browser context. For a firewall management interface, this is particularly concerning as administrators with elevated privileges are the primary users of this functionality.

The vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation), which covers cross-site scripting issues resulting from insufficient input validation and output encoding.

Root Cause

The root cause of this vulnerability is improper input validation and insufficient output encoding in the Endian Firewall web management interface. The application does not adequately sanitize user-supplied input in the remark parameter before storing it, nor does it properly encode the stored data when rendering it back to users in the browser. This allows HTML and JavaScript content to be interpreted and executed rather than displayed as harmless text.

Attack Vector

The attack requires network access to the Endian Firewall management interface and valid authentication credentials. An attacker with low-privilege access to the firewall's web interface navigates to /manage/ipsec/ and injects malicious JavaScript code into the remark field. This payload is stored on the server and subsequently delivered to any user who views the IPsec configuration page. The malicious script executes within the victim's browser session, enabling actions such as session token theft, administrative action execution on behalf of the victim, or redirection to phishing pages.

The attack mechanism involves submitting a crafted payload through the remark parameter that includes JavaScript code. When other users—particularly administrators—view the IPsec configuration page, the stored payload renders without proper encoding, causing the browser to execute the injected script with the victim's session privileges.

Detection Methods for CVE-2026-34820

Indicators of Compromise

• Unusual JavaScript code patterns or HTML tags present in IPsec configuration remarks within the Endian Firewall database
• Unexpected outbound connections from administrator browsers when accessing the /manage/ipsec/ page
• Reports of strange behavior or redirections when administrators access the firewall management interface
• Authentication tokens or session cookies being transmitted to external domains

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block XSS payloads targeting the /manage/ipsec/ endpoint
• Monitor HTTP POST requests to /manage/ipsec/ for suspicious payloads containing <script>, javascript:, event handlers, or encoded variants
• Review Endian Firewall access logs for anomalous patterns of access to the IPsec management pages
• Deploy browser-based security monitoring to detect unexpected script execution on the management interface

Monitoring Recommendations

• Enable detailed logging for all administrative actions within the Endian Firewall management interface
• Configure alerting for any modifications to IPsec configuration remarks, particularly those containing special characters or encoded content
• Implement Content Security Policy (CSP) reporting to detect inline script execution attempts
• Regularly audit stored configuration data for presence of HTML or JavaScript content

How to Mitigate CVE-2026-34820

Immediate Actions Required

• Restrict access to the Endian Firewall management interface to trusted networks and IP addresses only
• Review existing IPsec configuration remarks for any suspicious content or JavaScript code
• Implement network segmentation to limit exposure of the firewall management interface
• Consider enabling additional authentication factors for administrative access
• Deploy a web application firewall in front of the management interface to filter XSS payloads

Patch Information

At the time of publication, consult Endian Community Support for the latest security updates and patch availability. Review the VulnCheck Advisory on Endian Firewall for detailed vulnerability information and remediation guidance.

Workarounds

• Implement strict input validation on the remark parameter by removing or encoding HTML special characters before storage
• Deploy a reverse proxy with XSS filtering capabilities in front of the Endian Firewall management interface
• Limit administrative access to the firewall interface to a dedicated management VLAN accessible only from hardened jump hosts
• Implement Content Security Policy headers to prevent inline JavaScript execution in the management interface
• Regularly audit IPsec configuration entries and sanitize any existing remarks containing suspicious content

# Example: Restrict management interface access via iptables
# Allow only trusted management subnet to access web interface
iptables -A INPUT -p tcp --dport 443 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP

# Example: Add CSP header via reverse proxy (nginx)
# add_header Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none';" always;