CVE-2026-25885: PolarLearn Auth Bypass Vulnerability

CVE-2026-25885 Overview

CVE-2026-25885 is an Authorization Bypass vulnerability in PolarLearn, a free and open-source learning program. In version 0-PRERELEASE-16 and earlier, the group chat WebSocket endpoint at wss://polarlearn.nl/api/v1/ws can be accessed without authentication. An unauthenticated attacker can subscribe to any group chat by simply providing a group UUID and can send arbitrary messages to any group. The server accepts and persists these messages in the group's chatContent, making this a significant data integrity and confidentiality issue rather than just a visual spam problem.

Critical Impact

Unauthenticated attackers can read and write messages to any group chat in PolarLearn, compromising both confidentiality and integrity of educational communications.

Affected Products

• PolarLearn version 0-PRERELEASE-16 and earlier
• PolarLearn WebSocket API endpoint (/api/v1/ws)

Discovery Timeline

• 2026-02-09 - CVE-2026-25885 published to NVD
• 2026-02-10 - Last updated in NVD database

Technical Details for CVE-2026-25885

Vulnerability Analysis

This vulnerability stems from CWE-285 (Improper Authorization), where the WebSocket endpoint responsible for group chat functionality fails to verify that connecting clients are authenticated and authorized to access specific group resources. The WebSocket connection handler accepts subscription requests for any group UUID without validating the requester's identity or membership in that group.

When a client connects to the WebSocket endpoint and provides a group UUID, the server immediately grants access to the group's chat stream. This allows attackers to enumerate and access private group conversations across the entire platform. Furthermore, the server processes and stores messages sent by unauthenticated clients, permanently injecting attacker-controlled content into legitimate group discussions.

The attack is network-accessible with no prerequisites required—attackers need only knowledge of a valid group UUID, which could be obtained through enumeration, social engineering, or leaked URLs.

Root Cause

The root cause is the absence of authentication and authorization checks on the WebSocket connection handler. The server accepts WebSocket connections and processes subscription/message requests without verifying:

1. Whether the connecting client has a valid session or authentication token
2. Whether the authenticated user (if any) is a member of the requested group
3. Whether the user has appropriate permissions to read or write messages

This represents a fundamental design flaw where the WebSocket API was implemented without integrating with the application's authentication framework.

Attack Vector

The attack is executed over the network via the WebSocket protocol. An attacker can exploit this vulnerability by:

1. Establishing a WebSocket connection to wss://polarlearn.nl/api/v1/ws without any authentication credentials
2. Sending a subscription message with a target group's UUID to join the chat stream
3. Receiving all messages sent to that group in real-time
4. Sending malicious or misleading messages that are permanently stored in the group's chat history

The attack requires no user interaction and can be automated to monitor multiple groups simultaneously. Since group UUIDs follow a predictable format, attackers could potentially enumerate valid group identifiers.

Detection Methods for CVE-2026-25885

Indicators of Compromise

• WebSocket connections to /api/v1/ws from IP addresses not associated with authenticated user sessions
• Rapid subscription requests to multiple group UUIDs from a single source
• Messages appearing in group chats from users not enrolled in those groups
• Unusual volume of WebSocket connections without corresponding HTTP authentication requests

Detection Strategies

• Implement logging for all WebSocket connection attempts, including client IP, requested group UUID, and authentication state
• Monitor for WebSocket connections that lack session cookies or authentication tokens
• Alert on group chat messages where the sender UUID does not match any enrolled group member
• Correlate WebSocket activity with authentication logs to identify unauthenticated access attempts

Monitoring Recommendations

• Enable verbose logging on the WebSocket server to capture connection metadata
• Set up alerts for failed authentication patterns followed by successful WebSocket connections
• Review chat logs for messages from unknown or suspicious user identifiers
• Monitor network traffic for unusual WebSocket connection patterns targeting the /api/v1/ws endpoint

How to Mitigate CVE-2026-25885

Immediate Actions Required

• Upgrade PolarLearn to a version containing the security fix (commit 3ba588fda0d3f8e238483a20772719f27e52e79f)
• If immediate upgrade is not possible, consider temporarily disabling the WebSocket chat functionality
• Audit existing group chat histories for potentially injected malicious content
• Review access logs to determine if exploitation has already occurred

Patch Information

A fix for this vulnerability has been committed to the PolarLearn repository. The patch is available at the GitHub commit. Organizations running affected versions should apply this update immediately.

For detailed information about the vulnerability and remediation, refer to the GitHub Security Advisory GHSA-gvjm-5pw7-6c8c.

Workarounds

• Block external access to the WebSocket endpoint (/api/v1/ws) at the network or reverse proxy level until the patch can be applied
• Implement IP allowlisting to restrict WebSocket connections to trusted networks
• Deploy a Web Application Firewall (WAF) rule to require authentication headers on WebSocket upgrade requests
• Consider placing the WebSocket endpoint behind VPN access as a temporary measure