n8n: Prototype Pollution via VM Expression Engine Sandbox Escape Leads to Denial of Service

Impact

An authenticated user able to create or edit a workflow expression could abuse the expression engine's array-element access to obtain a reference to a host built-in and pollute its prototype in the main n8n process, leading to a denial of service.

Both self-hosted and cloud instances running the VM expression engine are affected.

Patches

The issue has been fixed in n8n versions 1.123.67, 2.31.5, and 2.32.1. 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.
• Disable the VM expression engine if an alternative is available for your deployment.

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