n8n: Prototype Pollution via Workflow Structure Summary Can Lead to Denial of Service

Impact

The Instance AI workflow summary built its result with get-or-create-then-nested-write idioms keyed by node names and connection keys taken from the stored workflow. Those are arbitrary strings: the restricted-name guard n8n shows in the editor is client-side and is bypassed by posting the workflow to the REST API directly. So a reserved key such as __proto__ resolved up the prototype chain instead of creating an own key, and the write landed on Object.prototype in the main n8n process, affecting every later request. The patch builds the summary with null-prototype accumulators and validates the keys it accepts, so reserved names cannot reach the prototype chain.

Patches

The issue has been fixed in n8n versions 2.37.7 and 2.38.2. 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.
• Remove or leave unconfigured the N8N_INSTANCE_AI_MODEL* environment variables to prevent the Instance AI module from reaching the vulnerable code path.
• Restart the n8n process to clear any in-memory prototype pollution if an attack is suspected.

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