SiYuan Note is a personal knowledge management system that, in versions 3.6.0 and earlier, contains a critical design flaw in its WebSocket endpoint (/ws). This endpoint was intended to keep the kernel alive on the login page by allowing connections with specific URL parameters (?app=siyuan&id=auth&type=auth) without authentication. However, this design inadvertently permits any external client, including malicious websites via cross-origin WebSocket connections, to establish a connection and receive all server push events in real-time. These events expose sensitive document metadata such as document titles, notebook names, file paths, and detailed CRUD (Create, Read, Update, Delete) operations performed by authenticated users. The vulnerability is exacerbated by the absence of Origin header validation, which normally restricts cross-origin requests, allowing attackers to silently connect to a victim's local SiYuan instance and monitor their note-taking activities without user interaction or authentication. This flaw corresponds to CWE-287 (Improper Authentication). The issue was addressed and fixed in SiYuan Note version 3.6.1. The CVSS 4.0 vector indicates network attack vector, low attack complexity, no privileges or user interaction required, and low impact on confidentiality, with no impact on integrity or availability.

The vulnerability allows attackers to bypass authentication and eavesdrop on sensitive user data in real-time, including document titles, notebook names, file paths, and all CRUD operations. This can lead to significant privacy violations, exposure of confidential information, and potential leakage of intellectual property or sensitive organizational data. Since the attack can be conducted silently via malicious websites exploiting cross-origin WebSocket connections, users may be unaware of the compromise. Organizations relying on SiYuan Note for sensitive knowledge management risk data leakage and espionage, especially if users access the application in environments where malicious websites can be visited. Although the vulnerability does not allow direct modification or deletion of data by attackers, the exposure of metadata and user activity can facilitate targeted social engineering, further attacks, or competitive intelligence gathering. The lack of authentication and Origin validation increases the attack surface, making exploitation feasible without user interaction or credentials.

Organizations and users should immediately upgrade SiYuan Note to version 3.6.1 or later, where this vulnerability is patched. Until upgrading, users should restrict access to the SiYuan Note WebSocket endpoint by implementing network-level controls such as firewall rules or local host restrictions to prevent external connections to the /ws endpoint. Browser security settings or extensions that block cross-origin WebSocket connections can reduce risk. Additionally, users should avoid visiting untrusted or malicious websites while SiYuan Note is running locally to mitigate cross-origin exploitation. Developers and administrators should verify that Origin header validation is enforced on WebSocket endpoints to prevent unauthorized cross-origin connections. Monitoring network traffic for unusual WebSocket connections and reviewing application logs for suspicious activity can help detect exploitation attempts. Finally, educating users about the risks of running vulnerable versions and visiting untrusted sites concurrently with SiYuan Note is important.