CVE-2026-34823: Endian Firewall Stored XSS Vulnerability

CVE-2026-34823 Overview

Endian Firewall version 3.3.25 and prior are vulnerable to a stored cross-site scripting (XSS) vulnerability via the remark parameter in the /manage/password/web/ endpoint. An authenticated attacker can inject arbitrary JavaScript code that persists in the application and executes whenever other users view the affected page. This vulnerability allows attackers to steal session tokens, perform actions on behalf of legitimate users, and potentially gain elevated privileges within the firewall management interface.

Critical Impact

Authenticated attackers can inject persistent JavaScript code into the Endian Firewall management interface, enabling session hijacking, credential theft, and administrative account compromise when other users access the affected page.

Affected Products

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

Discovery Timeline

• 2026-04-02 - CVE CVE-2026-34823 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-34823

Vulnerability Analysis

This stored cross-site scripting (CWE-79) vulnerability exists in the password management interface of Endian Firewall. The remark parameter in the /manage/password/web/ endpoint fails to properly sanitize user-supplied input before storing it in the application database. When this malicious content is subsequently rendered to other users viewing the page, the injected JavaScript executes in their browser context with full access to the session and DOM.

The attack requires authentication, meaning an attacker must first obtain valid credentials to exploit this vulnerability. However, once exploited, the stored payload persists and affects all users who access the vulnerable page, including administrators. This creates an opportunity for privilege escalation if a lower-privileged user can inject code that executes in an administrator's session.

Root Cause

The root cause of this vulnerability is improper input validation and output encoding in the Endian Firewall web management interface. The application fails to sanitize the remark parameter before storing user input in the database and does not properly encode output when rendering this data back to users. This allows HTML and JavaScript content to be stored and executed as part of the page content rather than being treated as plain text.

Attack Vector

The attack is network-based and requires an authenticated attacker to submit malicious JavaScript through the remark parameter to the /manage/password/web/ endpoint. The malicious payload is stored server-side and executes whenever another authenticated user navigates to the affected page. The attacker can craft payloads to exfiltrate session cookies, perform administrative actions, or redirect users to malicious sites.

The vulnerability exploitation flow involves:

1. An authenticated attacker accesses the password management interface
2. The attacker submits a crafted request containing JavaScript in the remark field
3. The malicious script is stored without sanitization
4. When other users (including administrators) view the page, the script executes
5. The attacker can harvest credentials, session tokens, or perform actions as the victim

Detection Methods for CVE-2026-34823

Indicators of Compromise

• HTTP POST requests to /manage/password/web/ containing script tags, event handlers (e.g., onerror, onload), or JavaScript protocol handlers in the remark parameter
• Unusual JavaScript payloads in firewall configuration data or database entries
• Unexpected outbound connections from client browsers after accessing the Endian Firewall management interface
• Session tokens being transmitted to unauthorized external domains

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect XSS payload patterns in requests to the Endian Firewall management interface
• Monitor HTTP traffic for requests to /manage/password/web/ containing suspicious characters or encoding patterns such as <script>, javascript:, or HTML event attributes
• Deploy browser-based security monitoring to detect unauthorized script execution in the firewall management context
• Review access logs for unusual patterns of authenticated requests to the password management endpoint

Monitoring Recommendations

• Enable verbose logging on the Endian Firewall web interface to capture all parameter values in requests
• Configure alerting for Content Security Policy (CSP) violations if implemented
• Monitor for data exfiltration attempts originating from browser sessions accessing the firewall management interface
• Establish baseline behavior for administrative interface usage and alert on deviations

How to Mitigate CVE-2026-34823

Immediate Actions Required

• Restrict access to the Endian Firewall management interface to trusted IP addresses only
• Implement network segmentation to limit who can access the /manage/password/web/ endpoint
• Review the remark fields in existing configurations for any suspicious or unexpected content
• Consider temporarily disabling or restricting access to the password management feature until a patch is available

Patch Information

No official patch information is currently available from the vendor. Organizations should monitor the Endian Community Help Center for security updates. Additional technical details can be found in the VulnCheck Advisory on Endian Firewall.

Workarounds

• Implement a reverse proxy with XSS filtering capabilities in front of the Endian Firewall management interface
• Deploy Content Security Policy (CSP) headers at the network edge to restrict script execution to trusted sources
• Limit the number of users with authentication credentials to the firewall management interface
• Use browser isolation technology when accessing the Endian Firewall administrative interface
• Conduct regular audits of stored configuration data to identify potentially malicious content

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