The vulnerability is a cross-site WebSocket hijacking flaw in the SiYuan Notes admin-only "/ws/network/proxy" endpoint. This weakness is classified as CWE-346. The server deliberately disables origin validation by making the CheckOrigin callback always return true, allowing any WebSocket connection from any origin to be accepted. An attacker can host a malicious webpage that an authenticated user visits; the page opens a WebSocket connection to the vulnerable endpoint and instructs the SiYuan kernel to proxy outbound traffic to attacker‑chosen destinations. This capability transfers internal traffic from the victim’s machine to arbitrary external or internal servers, effectively creating a covert tunnel for data exfiltration, reconnaissance, or lateral movement within the victim’s network.

SiYuan Notes versions prior to 3.7.4, including 3.7.3, are affected. The product is supplied by Siyuan‑Note and the vulnerable endpoint is intended for internal network proxy management but can be exploited by any authenticated user.

The CVSS score of 7.1 classifies the issue as high severity. The EPSS score of 0.00104 (~0.1%) indicates a very low probability of exploitation, and it is not listed in the CISA KEV catalog, suggesting no widespread exploitation yet. The exploitation requirements—a malicious page and an authenticated user—are relatively straightforward, making the attack vector likely to be feasible in environments where users can inadvertently visit rogue sites. Successful exploitation would allow the attacker to pivot traffic from the victim’s machine, potentially leaking sensitive data or accessing internal services.