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| Vulnerability ID | VCID-4axp-5smx-g7bc |
| Aliases |
CVE-2026-42236
GHSA-49m9-pgww-9vq6 |
| Summary | n8n Vulnerable to Unauthenticated Denial of Service via MCP Client Registration ## 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. |
| Status | Published |
| Exploitability | None |
| Weighted Severity | None |
| Risk | None |
| Affected and Fixed Packages | Package Details |
| System | Score | Found at |
|---|---|---|
| epss | 0.00165 | https://api.first.org/data/v1/epss?cve=CVE-2026-42236 |
| cvssv3.1 | 7.5 | https://github.com/n8n-io/n8n |
| cvssv4 | 8.7 | https://github.com/n8n-io/n8n |
| generic_textual | HIGH | https://github.com/n8n-io/n8n |
| cvssv3.1 | 7.5 | https://github.com/n8n-io/n8n/security/advisories/GHSA-49m9-pgww-9vq6 |
| cvssv4 | 8.7 | https://github.com/n8n-io/n8n/security/advisories/GHSA-49m9-pgww-9vq6 |
| generic_textual | HIGH | https://github.com/n8n-io/n8n/security/advisories/GHSA-49m9-pgww-9vq6 |
| ssvc | Track | https://github.com/n8n-io/n8n/security/advisories/GHSA-49m9-pgww-9vq6 |
| cvssv3.1 | 7.5 | https://nvd.nist.gov/vuln/detail/CVE-2026-42236 |
| cvssv4 | 8.7 | https://nvd.nist.gov/vuln/detail/CVE-2026-42236 |
| generic_textual | HIGH | https://nvd.nist.gov/vuln/detail/CVE-2026-42236 |
| Attack Vector (AV) | Attack Complexity (AC) | Privileges Required (PR) | User Interaction (UI) | Scope (S) | Confidentiality Impact (C) | Integrity Impact (I) | Availability Impact (A) |
|---|---|---|---|---|---|---|---|
network adjacent_network local physical |
low high |
none low high |
none required |
unchanged changed |
high low none |
high low none |
high low none |
| Attack Vector (AV) | Attack Complexity (AC) | Attack Requirements (AT) | Privileges Required (PR) | User Interaction (UI) | Vulnerable System Impact Confidentiality (VC) | Vulnerable System Impact Integrity (VI) | Vulnerable System Impact Availability (VA) | Subsequent System Impact Confidentiality (SC) | Subsequent System Impact Integrity (SI) | Subsequent System Impact Availability (SA) |
|---|---|---|---|---|---|---|---|---|---|---|
network adjacent local physical |
low high |
none present |
none low high |
none passive active |
high low none |
high low none |
high low none |
high low none |
high low none |
high low none |
| Attack Vector (AV) | Attack Complexity (AC) | Privileges Required (PR) | User Interaction (UI) | Scope (S) | Confidentiality Impact (C) | Integrity Impact (I) | Availability Impact (A) |
|---|---|---|---|---|---|---|---|
network adjacent_network local physical |
low high |
none low high |
none required |
unchanged changed |
high low none |
high low none |
high low none |
| Attack Vector (AV) | Attack Complexity (AC) | Attack Requirements (AT) | Privileges Required (PR) | User Interaction (UI) | Vulnerable System Impact Confidentiality (VC) | Vulnerable System Impact Integrity (VI) | Vulnerable System Impact Availability (VA) | Subsequent System Impact Confidentiality (SC) | Subsequent System Impact Integrity (SI) | Subsequent System Impact Availability (SA) |
|---|---|---|---|---|---|---|---|---|---|---|
network adjacent local physical |
low high |
none present |
none low high |
none passive active |
high low none |
high low none |
high low none |
high low none |
high low none |
high low none |
| Attack Vector (AV) | Attack Complexity (AC) | Privileges Required (PR) | User Interaction (UI) | Scope (S) | Confidentiality Impact (C) | Integrity Impact (I) | Availability Impact (A) |
|---|---|---|---|---|---|---|---|
network adjacent_network local physical |
low high |
none low high |
none required |
unchanged changed |
high low none |
high low none |
high low none |
| Attack Vector (AV) | Attack Complexity (AC) | Attack Requirements (AT) | Privileges Required (PR) | User Interaction (UI) | Vulnerable System Impact Confidentiality (VC) | Vulnerable System Impact Integrity (VI) | Vulnerable System Impact Availability (VA) | Subsequent System Impact Confidentiality (SC) | Subsequent System Impact Integrity (SI) | Subsequent System Impact Availability (SA) |
|---|---|---|---|---|---|---|---|---|---|---|
network adjacent local physical |
low high |
none present |
none low high |
none passive active |
high low none |
high low none |
high low none |
high low none |
high low none |
high low none |
| Percentile | 0.37309 |
| EPSS Score | 0.00165 |
| Published At | June 5, 2026, 12:55 p.m. |
| Date | Actor | Action | Source | VulnerableCode Version |
|---|---|---|---|---|
| 2026-06-04T16:51:38.347907+00:00 | GithubOSV Importer | Import | https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/04/GHSA-49m9-pgww-9vq6/GHSA-49m9-pgww-9vq6.json | 38.6.0 |