CVE-2026-86076: n8n: Expression Sandbox Escape via Class-Field Sanitizer Rebinding Can Lead to Code Execution

n8n's expression compiler runs a sanitizer that resolved through a dynamically scoped this. A class field named __sanitize could rebind it, which let the expression reach the Function constructor and build arbitrary code. The fix rejects reserved class-member names.

Two outcomes follow. On the backend, any expression author can run code in the n8n process, which holds the instance's stored credentials and can reach the host and network. In the editor preview, a member's expression can run as JavaScript in the browser session of whoever opens that workflow, so a low-privilege member can target an administrator.

The attacker needs an account that can create or edit workflows (low privileges in the CVSS 4.0 vector, with a present attack requirement). Scope impact is high on a subsequent system. Teams that let many users edit workflows, or that run AI agent nodes whose parameters come from expressions, should treat this as a priority.

Affected: n8n before 1.123.76; 2.0.0 up to but not including 2.37.7; and 2.38.0 and 2.38.1. Check your version:

n8n --version

For Docker, check the image tag. For npm: npm ls n8n. Instances where only fully trusted users can create or edit workflows have lower exposure.

Upgrade to n8n 1.123.76, 2.37.7 or 2.38.2, or later, on your release line.

npm install -g [email protected]

Temporary mitigations from n8n: restrict instance access to fully trusted users, avoid granting workflow-create or workflow-edit rights to untrusted users, audit existing workflows for unfamiliar expressions in node parameters, and set N8N_EXPRESSION_ENGINE=vm. These do not fully remove the risk.

Audit workflows for expressions containing class definitions with a field named __sanitize, or other unusual code inside {{ }} blocks. Review which users created or edited workflows recently. On the host, look for unexpected child processes, outbound connections or file changes from the n8n process. If an admin opened a suspect workflow in the editor, consider rotating the credentials that session could reach.

Impact

The expression compiler's sanitizer resolved through a dynamically-scoped this, so a class field named __sanitize rebound it and reached the Function constructor. On the backend, any expression author could run code in the n8n process; in the editor preview, a member's expression could run as JavaScript in the session of whoever opened the workflow. The patch rejects reserved class-member names.

Patches

The issue has been fixed in n8n versions 1.123.76, 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.
• Avoid granting workflow-create or workflow-edit permissions to untrusted users.
• Audit existing workflows for unexpected or unfamiliar expressions in node parameters.
• Set N8N_EXPRESSION_ENGINE=vm.

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