n8n before 1.123.67, 2.31.5, and 2.32.1 contains a prototype pollution vulnerability in the VM expression engine. An authenticated user able to create or edit a workflow expression can abuse the engine's array-element access to obtain a reference to a host built-in and pollute its prototype in the main n8n process (a sandbox escape), leading to a denial of service. Both self-hosted and cloud instances running the VM expression engine are affected.