n8n EUVD-2026-56139

Exploitation requires an authenticated n8n user account with permission to create and execute workflows - specifically, the ability to configure and run an Edit Fields (Set) node with an arbitrary field name. The attacker must be able to supply a dot-notation field name that resolves through the JavaScript prototype chain (e.g., paths beginning with __proto__ or constructor.prototype). No elevated privileges, admin access, or special n8n roles are required beyond basic workflow execution access. Exploitation is limited by: (1) authentication - unauthenticated access is not sufficient, as PR:L in the CVSS vector confirms; (2) workflow execution permissions - accounts that have been explicitly denied workflow creation or execution cannot trigger this; and (3) the impact is strictly availability (instance-wide DoS) with no confidentiality or integrity compromise per the CVSS vector. There is no dependency on non-default configuration - any default n8n instance with at least one non-admin user account is at risk.

The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N, score 7.1) correctly characterizes this as a network-reachable, low-complexity, low-privilege attack with high availability impact and no confidentiality or integrity compromise. The low-privilege requirement (PR:L) is the single gating condition: any authenticated n8n user with workflow creation or execution access can trigger this deterministically. The impact is maximally disruptive for availability - the entire instance fails for all users - but bounded in scope to the n8n process itself with no data exfiltration or integrity risk per the vector. No EPSS score was provided in the input data, and the vulnerability does not appear in the CISA KEV catalog, indicating no confirmed widespread active exploitation at time of analysis. However, the extremely low attack complexity and deterministic, instance-wide impact mean the real-world operational risk is high for any n8n deployment with untrusted or semi-trusted authenticated users. The absence of a KEV listing should not be read as low urgency: the attack requires no special tooling, produces an obvious and repeatable effect, and the fix is readily available.

An authenticated n8n user with standard workflow permissions creates a new workflow, adds an Edit Fields (Set) node, and configures an output field with a dot-notation prototype pollution path such as __proto__.verify targeting a property used in the authentication middleware. Upon executing the workflow, the path setter traverses the prototype chain and overwrites the property on the global Object prototype in the main Node.js process. Every subsequent authenticated HTTP request to the n8n instance then fails, effectively performing an instance-wide denial of service that persists until an administrator manually restarts the process.