CVE-2026-27178: MajorDoMo Stored XSS Vulnerability

CVE-2026-27178 Overview

CVE-2026-27178 is a stored cross-site scripting (XSS) vulnerability in MajorDoMo (Major Domestic Module), a popular home automation platform. The vulnerability exists in the shoutbox functionality where user-supplied parameters are injected and stored without proper sanitization. An unauthenticated attacker can exploit the /objects/?method= endpoint to execute stored methods with attacker-controlled parameters, leading to persistent XSS attacks that automatically execute when administrators view the dashboard.

Critical Impact

Unauthenticated attackers can inject malicious scripts that execute automatically every 3 seconds when administrators load the dashboard, enabling session hijacking through cookie exfiltration.

Affected Products

• MajorDoMo (Major Domestic Module) - All versions prior to patch

Discovery Timeline

• 2026-02-18 - CVE-2026-27178 published to NVD
• 2026-02-19 - Last updated in NVD database

Technical Details for CVE-2026-27178

Vulnerability Analysis

This stored XSS vulnerability represents a critical security weakness in MajorDoMo's input handling architecture. The attack chain begins at the /objects/?method= endpoint, which permits unauthenticated execution of stored methods with attacker-controlled parameters. Default methods such as ThisComputer.VolumeLevelChanged pass the user-supplied VALUE parameter directly into the say() function without any validation or encoding.

The say() function stores the message raw in the shouts database table without proper escaping or sanitization. When the shoutbox widget renders these stored messages, it does so without sanitization in both the PHP rendering code and HTML templates. The auto-refresh mechanism of the dashboard widget, which updates every 3 seconds, ensures that injected scripts execute automatically when any administrator loads the dashboard.

Root Cause

The root cause of CVE-2026-27178 is a complete lack of input sanitization at multiple points in the data flow. First, the /objects/?method= endpoint accepts and processes parameters from unauthenticated users without validation. Second, the say() function stores raw, unsanitized input directly into the database. Third, the shoutbox widget renders stored content without HTML encoding or output escaping. This combination of missing input validation and output encoding creates a classic stored XSS vulnerability pattern (CWE-79).

Attack Vector

The attack leverages the network-accessible endpoint to inject malicious JavaScript payloads. An attacker can craft a request to the /objects/?method= endpoint using a default method like ThisComputer.VolumeLevelChanged and include a malicious script in the VALUE parameter. This payload is stored in the database and executed in the browser context of any administrator who views the dashboard. Because the dashboard auto-refreshes frequently, the attack provides persistent access to administrator sessions, enabling cookie exfiltration and session hijacking without requiring any user interaction beyond normal dashboard usage.

For detailed technical analysis and proof-of-concept information, refer to the Chocapikk Blog Post and the VulnCheck Advisory.

Detection Methods for CVE-2026-27178

Indicators of Compromise

• Unexpected entries in the shouts database table containing <script> tags or JavaScript event handlers
• HTTP requests to /objects/?method= containing encoded script payloads or HTML special characters
• Administrator session cookies being exfiltrated to external domains
• Unusual network traffic from the MajorDoMo server to unknown external endpoints

Detection Strategies

• Monitor web server access logs for requests to /objects/?method= endpoints from untrusted IP addresses
• Implement database monitoring to detect insertion of HTML/JavaScript content in the shouts table
• Deploy web application firewall (WAF) rules to detect XSS payloads in method parameters
• Use Content Security Policy (CSP) violation reporting to identify script injection attempts

Monitoring Recommendations

• Enable detailed logging for all requests to the /objects/ endpoint
• Configure alerts for database changes to the shouts table containing suspicious content
• Monitor for outbound connections from the MajorDoMo server that may indicate data exfiltration
• Review administrator session activity for signs of hijacking or unauthorized access

How to Mitigate CVE-2026-27178

Immediate Actions Required

• Apply the security patch from GitHub Pull Request #1177
• Restrict access to the /objects/?method= endpoint to authenticated users only
• Review and sanitize existing content in the shouts database table
• Implement network-level access controls to limit exposure of the MajorDoMo interface

Patch Information

A fix has been submitted via GitHub Pull Request #1177 for the MajorDoMo project. Organizations should apply this patch immediately to address the stored XSS vulnerability. The patch implements proper input sanitization and output encoding in the affected code paths.

Workarounds

• Disable the shoutbox widget on the dashboard until the patch is applied
• Implement a web application firewall (WAF) rule to block XSS payloads in requests to /objects/
• Restrict network access to the MajorDoMo interface to trusted IP addresses only
• Clear the shouts database table and monitor for new malicious entries

# Example: Restrict access to the objects endpoint using .htaccess
<Location /objects/>
    Require ip 192.168.1.0/24
    Require ip 10.0.0.0/8
</Location>