Executive brief
n8n is an open-source workflow automation platform. A flaw in the Instance AI workflow summary feature allows authenticated users to modify object prototypes via specially crafted API requests, disrupting service availability for all users. While exploitation requires a valid n8n account, the vulnerability impacts all subsequent operations on the server.
Technical details
This is a prototype pollution vulnerability (CWE-1321) in n8n's Instance AI workflow summary builder. The vulnerable code constructs summary objects using node names and connection keys taken directly from stored workflows via get-or-create-then-nested-write patterns. Although the web editor enforces client-side restrictions on key names, an attacker with valid credentials can bypass this by posting directly to the REST API with reserved property names such as `__proto__`, `constructor`, or `prototype`. When these keys are used as object property names without validation, they resolve up the prototype chain rather than creating own properties, causing writes to land on Object.prototype in the main n8n process. This pollution persists in memory and affects every subsequent request. The fix validates key names and uses null-prototype accumulators (Object.create(null)) to prevent prototype chain pollution. Patches are available in versions 2.37.7 and 2.38.2 or later.
Affected products
- n8n n8n < 2.37.7 and >= 2.38.0, < 2.38.2
Timeline
- 2026-09-02: disclosed: Vulnerability published to GitHub Advisory Database
- 2026-09-10: patched: Patches released in n8n 2.37.7 and 2.38.2