CVE-2026-3951: LockerProject Locker XSS Vulnerability

CVE-2026-3951 Overview

A Cross-Site Scripting (XSS) vulnerability has been discovered in LockerProject Locker affecting versions 0.0.0, 0.0.1, and 0.1.0. The vulnerability exists in the authIsAwesome function within the file source-code/Locker-master/Ops/registry.js, specifically in the Error Response Handler component. An attacker can manipulate the ID argument to inject malicious scripts, enabling remote exploitation. The exploit has been publicly disclosed, and the project maintainers have been notified through an issue report but have not yet responded.

Critical Impact
Remote attackers can inject malicious scripts through the ID parameter, potentially leading to session hijacking, credential theft, and unauthorized actions on behalf of authenticated users.

Affected Products

LockerProject Locker version 0.0.0
LockerProject Locker version 0.0.1
LockerProject Locker version 0.1.0

Discovery Timeline

2026-03-11 - CVE CVE-2026-3951 published to NVD
2026-03-12 - Last updated in NVD database

Technical Details for CVE-2026-3951

Vulnerability Analysis

This vulnerability is classified as Cross-Site Scripting (CWE-79), where user-supplied input is improperly handled within the Error Response Handler component. The authIsAwesome function in registry.js fails to properly sanitize the ID argument before including it in error response output. This allows an attacker to inject arbitrary JavaScript code that executes in the context of the victim's browser session.

The vulnerability can be exploited remotely without authentication, though user interaction is required for successful exploitation. When a user clicks a malicious link or visits a compromised page, the injected script executes with the privileges of the victim user, potentially compromising their session or extracting sensitive information.

Root Cause

The root cause of this vulnerability is insufficient input validation and output encoding in the Error Response Handler. The authIsAwesome function directly incorporates the ID parameter into the response without proper sanitization, allowing HTML and JavaScript content to be rendered in the browser. This violates secure coding practices for handling user-controlled input in web applications.

Attack Vector

The attack vector is network-based, requiring an attacker to craft a malicious URL or form submission containing XSS payloads in the ID parameter. When a victim interacts with the malicious content, the injected script executes in their browser context. This is a reflected XSS vulnerability where the malicious payload is immediately returned in the error response.

The vulnerability allows attackers to:

Steal session cookies and authentication tokens
Perform actions on behalf of the authenticated user
Redirect users to malicious websites
Deface the application interface
Capture keystrokes and form inputs

Additional technical details can be found in the GitHub Locker Issue #963 and VulDB #350383 Report.

Detection Methods for CVE-2026-3951

Indicators of Compromise

Unusual URL parameters containing script tags, event handlers, or encoded JavaScript payloads targeting the ID parameter
Web server logs showing requests with XSS attack patterns such as <script>, javascript:, onerror=, or onload= in the ID parameter
Client-side reports of unexpected JavaScript execution or browser security warnings

Detection Strategies

Implement Web Application Firewall (WAF) rules to detect and block common XSS patterns in request parameters
Deploy Content Security Policy (CSP) headers to restrict script execution sources and detect policy violations
Enable browser-based XSS auditors and monitor for triggered protections
Review application logs for requests to registry.js endpoints with suspicious parameter values

Monitoring Recommendations

Monitor network traffic for requests containing encoded script payloads or XSS attack signatures
Configure alerting for unusual patterns in error response generation from the Error Response Handler component
Implement real-time log analysis to detect potential exploitation attempts against the vulnerable endpoint

How to Mitigate CVE-2026-3951

Immediate Actions Required

Review and restrict access to the affected Error Response Handler endpoint until a patch is available
Implement input validation to sanitize the ID parameter, rejecting or encoding special characters
Deploy Content Security Policy headers to mitigate the impact of potential XSS exploitation
Consider disabling or removing the affected authIsAwesome function if it is not critical to application functionality

Patch Information

No official patch has been released by the LockerProject maintainers at this time. The project was informed of the vulnerability through GitHub Locker Issue #963 but has not yet responded. Users should monitor the GitHub Locker Project Repository for updates and security advisories.

Workarounds

Implement server-side input validation to sanitize or reject malicious input in the ID parameter before processing
Apply output encoding (HTML entity encoding) when rendering the ID parameter in error responses
Deploy a Web Application Firewall (WAF) with XSS filtering rules to block attack attempts at the network perimeter
Implement strict Content Security Policy headers with script-src 'self' to prevent inline script execution

bash

# Example Content Security Policy header configuration for Apache
# Add to .htaccess or httpd.conf
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none'; frame-ancestors 'self'"

# Example for Nginx
# Add to server block in nginx.conf
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none'; frame-ancestors 'self'";