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High

n8n Vulnerable to Unauthenticated Denial of Service via MCP Client Registration

  • Disclosed: 29.04.2026
  • Updated: 11.10.2026 10:22

Impact

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.

The patches address the unbound registration with an upper bound of registered clients and disabling creation when MCP is disabled on the instance. Mean to restrict the payload size of requests already exist and can be used to control additional risks.

Patches

The issue has been fixed in n8n versions 1.123.32, 2.17.4, and 2.18.1. 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 network access to the n8n instance to prevent requests from untrusted sources.
  • Reduce the maximum accepted payload size by lowering the N8N_PAYLOAD_SIZE_MAX environment variable from its default value.

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

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
npm package n8n < 1.123.32, >= 2.18.0, < 2.18.1, >= 2.0.0, < 2.17.4 1.123.32, 2.18.1, 2.17.4

References

CVSS score 7.5/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE)
CWE-770
Platform
npm
Package
n8n
Disclosed
29.04.2026
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-49m9-pgww-9vq6 - CC BY 4.0

Vulnerability history: n8n

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (156) in the archive
Total entries
156
First → latest
05.2023 09.2026
Without a fix
1
Exploited in attacks
1

Severity breakdown

  • Critical 24
  • High 58
  • Medium 74

Disclosures per year

Severity:
  1. n8n Vulnerable to Unauthenticated Denial of Service via MCP Client Registration this entry
    High · 7.5 CVE-2026-42236 < 1.123.32, >= 2.18.0, < 2.18.1, >= 2.0.0, < 2.17.4 1.123.32, 2.18.1, 2.17.4
  2. n8n: Expression Sandbox Escape via Shared Builtin Tampering and Code-Printer Injection Leads to Code Execution
    High CVE-2026-86083 < 1.123.76, >= 2.38.0, < 2.38.2, >= 2.0.0, < 2.37.7 1.123.76, 2.38.2, 2.37.7
  3. n8n: Domain-Restriction Bypass via Unguarded Model-Search Endpoint in OpenAI Chat Model Node
    High CVE-2026-86082 < 1.123.76, >= 2.38.0, < 2.38.2, >= 2.0.0, < 2.37.7 1.123.76, 2.38.2, 2.37.7
  4. n8n: Regular Expression Denial of Service in the Default Blocked-File-Pattern Match via a Git Node Clone Path
    High CVE-2026-86081 < 1.123.76, >= 2.38.0, < 2.38.2, >= 2.0.0, < 2.37.7 1.123.76, 2.38.2, 2.37.7
  5. n8n: Unauthenticated Persistent Storage Exhaustion via OAuth Dynamic Client Registration Endpoint
    High CVE-2026-86075 >= 2.38.0, < 2.38.2, < 2.37.7 2.38.2, 2.37.7
  6. n8n: Expression Sandbox Escape via Class-Field Sanitizer Rebinding Can Lead to Code Execution
    High CVE-2026-86076 < 1.123.76, >= 2.38.0, < 2.38.2, >= 2.0.0, < 2.37.7 1.123.76, 2.38.2, 2.37.7
  7. n8n: Prototype Pollution via Dot-Notation Field Names Leads To Instance-Wide Denial of Service
    High CVE-2026-72749 < 1.123.67, >= 2.32.0, < 2.32.1, >= 2.0.0-rc.0, < 2.31.5 1.123.67, 2.32.1, 2.31.5
  8. n8n: Edit Image Node Format Injection Allows Arbitrary File Write
    High CVE-2026-72762 < 1.123.67, >= 2.32.0, < 2.32.1, >= 2.0.0-rc.0, < 2.31.5 1.123.67, 2.32.1, 2.31.5
  9. n8n: Shared-Workflow Editor Can Exfiltrate Credentials via Inline Sub-Workflow JSON
    High CVE-2026-72763 < 1.123.67, >= 2.32.0, < 2.32.1, >= 2.0.0-rc.0, < 2.31.5 1.123.67, 2.32.1, 2.31.5
  10. n8n: Credential Authorization Bypass via Expression in HTTP Request Node `genericAuthType`
    High CVE-2026-72774 < 1.123.67, >= 2.32.0, < 2.32.1, >= 2.0.0-rc.0, < 2.31.5 1.123.67, 2.32.1, 2.31.5
  11. n8n: Expression sandbox escape via arrow-function bodies enabling command execution
    High CVE-2026-72765 >= 2.32.0, < 2.32.1, < 2.31.5 2.32.1, 2.31.5
  12. n8n: Send Email Node Arbitrary File Read and SSRF via Nodemailer Content-Object Type Confusion
    High CVE-2026-72766 < 1.123.67, >= 2.32.0, < 2.32.1, >= 2.0.0-rc.0, < 2.31.5 1.123.67, 2.32.1, 2.31.5
  13. n8n: Authenticated code execution in the n8n Git node
    High CVE-2026-72767 < 1.123.67, >= 2.32.0, < 2.32.1, >= 2.0.0-rc.0, < 2.31.5 1.123.67, 2.32.1, 2.31.5
  14. n8n: Git Node fetch/pull/pushTags Operations Bypass Sandbox Path Restriction
    High CVE-2026-72770 < 1.123.67, >= 2.32.0, < 2.32.1, >= 2.0.0-rc.0, < 2.31.5 1.123.67, 2.32.1, 2.31.5
  15. n8n: Bypass "Allowed HTTP Request Domains" Credential Restriction in Multiple AI and LLM Nodes
    High CVE-2026-72771 >= 2.32.0, < 2.32.1, < 2.31.5 2.32.1, 2.31.5
  16. n8n: Account Takeover via Unverified Email Claim in Token Exchange Embed Login
    High CVE-2026-72772 >= 2.32.0, < 2.32.1, < 2.31.5 2.32.1, 2.31.5
  17. n8n: SSO Instance-Role Provisioning Allows Privilege Escalation to Instance Owner
    High CVE-2026-65016 < 1.123.64, >= 2.30.0, < 2.30.1, >= 2.0.0-rc.0, < 2.29.8 1.123.64, 2.30.1, 2.29.8
  18. n8n: Legacy Expression Evaluator Sanitizer Bypass Leads to Authenticated Code Execution
    High CVE-2026-65591 < 1.123.64, >= 2.30.0, < 2.30.1, >= 2.0.0-rc.0, < 2.29.8 1.123.64, 2.30.1, 2.29.8
  19. n8n: Privilege Escalation and Code Execution via Full Public API Key Scope Assignment to Token Exchange JWTs
    High CVE-2026-65595 >= 2.30.0, < 2.30.1, < 2.29.8 2.30.1, 2.29.8
  20. n8n: Cross-Issuer Token Exchange Account Binding via Subject-Only Identity Resolution
    High CVE-2026-59208 >= 2.28.0, < 2.28.1, < 2.27.4 2.28.1, 2.27.4
  21. n8n: "Allowed HTTP Request Domains" Restriction Bypass via AI Agents MCP Connector
    High CVE-2026-59207 >= 2.28.0, < 2.28.1, < 2.27.4 2.28.1, 2.27.4
Show more (20) Showing 21 of 82

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