CVE-2026-72749: n8n Prototype Pollution DoS Vulnerability

CVE-2026-72749 Overview

CVE-2026-72749 is a prototype pollution vulnerability in n8n, an open-source workflow automation platform. The flaw resides in the Edit Fields (Set) node, which assigns output fields via a dot-notation path setter without restricting the field name. An authenticated user can name a field after an inherited built-in method path and corrupt a shared global in the main Node.js process. Because that global is referenced on the request-authentication path, the instance then rejects every authenticated request. The result is an instance-wide denial of service affecting all users until the process is restarted. The issue is tracked under [CWE-1321] (Improperly Controlled Modification of Object Prototype Attributes).

Critical Impact
A single authenticated workflow can pollute the Node.js global prototype, breaking authentication for the entire n8n instance and forcing a process restart to restore service.

Affected Products

n8n versions prior to 1.123.67
n8n versions prior to 2.31.5
n8n versions prior to 2.32.1

Discovery Timeline

2026-08-11 - CVE-2026-72749 published to NVD
2026-08-11 - Last updated in NVD database

Technical Details for CVE-2026-72749

Vulnerability Analysis

The Edit Fields (Set) node in n8n allows workflow authors to construct output objects using dot-notation field paths. The node's setter walks the path and assigns values without validating whether any segment collides with an inherited property of Object.prototype. When a crafted field name traverses __proto__, constructor, or prototype, the write lands on the shared prototype chain rather than on the intended output object.

Because n8n runs as a single Node.js process, that polluted prototype is visible to every subsequent request handler. The vulnerability escalates from local object corruption to service-wide impact because n8n's request-authentication logic reads a global that the pollution overwrites. Every authenticated call then fails until the operator restarts the process. Authentication is required, but any low-privilege user permitted to build or execute workflows can trigger the condition.

Root Cause

The root cause is unsafe recursive property assignment in the Set node's dot-notation handler. The setter does not enforce an allowlist of writable keys and does not distinguish hasOwnProperty targets from inherited members. This pattern maps directly to [CWE-1321], where user-controlled input reaches an object write that traverses the prototype chain.

Attack Vector

Exploitation requires an authenticated n8n account with permission to edit or run workflows. The attacker adds a Set node whose field name specifies a prototype path, then executes the workflow. Execution corrupts a shared global consumed by the authentication middleware, after which the instance rejects all authenticated traffic. See the GitHub Security Advisory and the VulnCheck Advisory: Prototype Pollution for further technical details.

Detection Methods for CVE-2026-72749

Indicators of Compromise

Sudden failure of all authenticated API and UI requests to an n8n instance without a preceding deployment change.
Workflow execution logs showing Set node field names containing __proto__, constructor, or prototype segments.
Recovery of service only after restarting the n8n Node.js process, with the issue recurring when the malicious workflow runs again.

Detection Strategies

Audit stored workflow definitions for Set node parameters whose field paths include prototype-related tokens.
Correlate spikes in HTTP 401/403 responses from the n8n API with recent workflow executions performed by non-administrator accounts.
Alert on unexpected n8n process restarts, which are a strong signal that operators are recovering from prototype pollution.

Monitoring Recommendations

Ship n8n application logs and reverse-proxy access logs to a centralized logging platform for correlation with workflow execution events.
Monitor authentication middleware error rates and set thresholds that flag instance-wide auth failure within short intervals.
Track workflow edit and creation events by user, focusing on newly added Set nodes with unusual field naming patterns.

How to Mitigate CVE-2026-72749

Immediate Actions Required

Upgrade to n8n 1.123.67, 2.31.5, or 2.32.1 or later on the matching release branch.
Review recent workflow changes for Set nodes that reference prototype paths and remove or disable the offending workflows.
Restrict workflow creation and edit permissions to trusted operators until the upgrade is complete.

Patch Information

n8n has released fixed builds in versions 1.123.67, 2.31.5, and 2.32.1. The fix constrains the Set node's dot-notation field setter so that inherited prototype properties cannot be written. Refer to the GitHub Security Advisory for release notes and upgrade guidance.

Workarounds

Temporarily disable the Edit Fields (Set) node for untrusted users through role-based access controls where available.
Place the n8n instance behind an authenticated reverse proxy that can enforce request-level rate limits and workflow-execution quotas.
Establish a scheduled health check that restarts the n8n process on authentication failure spikes to reduce downtime while patching is in progress.

bash

# Verify installed n8n version and upgrade via npm
n8n --version
npm install -g n8n@1.123.67
# or, for the 2.x branch
npm install -g n8n@2.32.1