Missing Origin Validation in WebSockets

Summary

Bokeh is an interactive visualisation library written in Python. In versions through 3.8.1, and 3.9.x through 3.9.0.dev4, if a server is configured with an allowlist (e.g., dashboard.corp), an attacker can register a domain like dashboard.corp.attacker.com (or use a subdomain if applicable) and lure a victim to visit it. The malicious site can then initiate a WebSocket connection to the vulnerable Bokeh server. Since the Origin header (e.g., http://dashboard.corp.attacker.com/) matches the allowlist according to the flawed logic, the connection is accepted. Once connected, the attacker can interact with the Bokeh server on behalf of the victim, potentially accessing sensitive data or modifying visualisations. This issue is fixed in version 3.8.2.