CVE-2026-74802: SiYuan: Cross-Site WebSocket Hijacking on the admin-only network proxy endpoint (`/ws/network/proxy`) via explicit `CheckOrigin: true` bypass

/ws/network/proxy is an admin-only WebSocket forward-proxy endpoint (target URL and headers fully attacker-specifiable via query parameters). Its websocket.Upgrader explicitly overrides CheckOrigin to unconditionally return true — disabling the origin validation that the gorilla/websocket library otherwise enforces by default. WebSocket handshake requests are not subject to CORS preflight at all (unlike fetch/XHR), so origin validation for WebSocket endpoints has to be done deliberately by the server; here it has been deliberately turned off instead. Combined with the endpoint’s own query-parameter-driven proxy target, this is a textbook Cross-Site WebSocket Hijacking (CSWSH) primitive on a capability that amounts to an authenticated network pivot through the SiYuan kernel process.