n8n: Send-and-Wait HMAC Bypass Allows Unauthenticated Approval of Waiting Executions

Impact

The waiting-webhook endpoint accepts a Send-and-Wait node reference in two forms. It decided which validation to apply before normalising the second form, so a request in that shape was accepted without the signature approvals require. A caller holding an execution's resume token can release an approval intended for someone else; everything downstream then runs under the workflow owner's credentials, which depending on the workflow can reach command execution.

Patches

The issue has been fixed in n8n versions 2.42.1 and 2.41.4. Users should upgrade to one of these versions or later to remediate the vulnerability.

Workarounds

If upgrading is not immediately possible, administrators should consider the following temporary mitigations:

• Restrict n8n instance access to fully trusted users only.
• Avoid using Send-and-Wait nodes that gate high-consequence actions in workflows where an earlier public, unauthenticated trigger node exposes a resumeToken to external callers.
• Restrict or disable public webhook and chat trigger endpoints that precede Send-and-Wait approval nodes until the instance is patched.

These workarounds do not fully remediate the risk and should only be used as short-term mitigation measures.