CVE-2026-54069: SiYuan: Unauthenticated Admin API Access via Blanket chrome-extension:// Origin Allowlist

Synopsis

An authentication bypass in SiYuan Note's kernel HTTP server allows any installed Chrome or Chromium browser extension to make fully authenticated administrator API calls to the local SiYuan service without credentials. The server unconditionally trusts all chrome-extension:// origins and, combined with the default empty access code on desktop installs, any extension (including one compromised via supply chain attack) can reach the API over localhost with no authentication required. Successful exploitation enables full read and write access to the user's notes, including data exfiltration, stored XSS injection, and configuration tampering. HarborGuard tracks this advisory and will make a patched-image rebuild available the moment an upstream fix is published.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The attacker's payload reaches the SiYuan kernel HTTP server over the network (localhost on the victim's machine), so the service must be running and reachable from the browser context.

• AuthenticationNot required

  No credentials are needed; the server grants RoleAdministrator access to any chrome-extension:// origin without any authentication check, and the default AccessAuthCode is empty on desktop installs.

• Victim interactionNot required

  No user action beyond having a malicious or compromised extension installed is required; the extension can initiate API calls silently in the background.

• Attack complexityDetail

  Attack complexity is rated High, reflecting the environmental precondition that a malicious or supply-chain-compromised Chrome/Chromium extension must already be installed in the victim's browser.

Blast Radius

• Reads and exfiltrates all notes, attachments, and stored data from the SiYuan knowledge base.
• Injects stored XSS payloads into note content that execute in the SiYuan desktop or browser interface.
• Modifies or deletes SiYuan configuration, including sync settings, access codes, and workspace paths.
• Tampers with persisted notebook and document structure, causing data loss or corruption.