n8n-io n8n up to 1.123.31/2.17.3/2.18.0 MCP client_name cross site scripting

Summaryinfo

A vulnerability was found in n8n-io n8n up to 1.123.31/2.17.3/2.18.0 and classified as problematic. Impacted is an unknown function of the component MCP Handler. Executing a manipulation of the argument client_name can lead to cross site scripting. This vulnerability is handled as CVE-2026-42235. The attack can be executed remotely. There is not any exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability classified as problematic was found in n8n-io n8n up to 1.123.31/2.17.3/2.18.0. This vulnerability affects an unknown code of the component MCP Handler. The manipulation of the argument client_name with an unknown input leads to a cross site scripting vulnerability. The CWE definition for the vulnerability is CWE-87. The product does not neutralize or incorrectly neutralizes user-controlled input for alternate script syntax. As an impact it is known to affect integrity. CVE summarizes:

n8n is an open source workflow automation platform. Prior to versions 1.123.32, 2.17.4, and 2.18.1, an unauthenticated attacker could register a malicious MCP OAuth client with a crafted client_name. If a victim user authorized the OAuth consent dialog and a second user subsequently revoked that access, a toast notification would render the injected script. Clicking the link would execute arbitrary JavaScript in the victim's authenticated n8n browser session, enabling credential and session token theft, workflow manipulation, or privilege escalation. This issue has been patched in versions 1.123.32, 2.17.4, and 2.18.1.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-42235 since 04/25/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1059.007.

Upgrading to version 1.123.32, 2.17.4 or 2.18.1 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-27110). Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

• n8n-io

Name

• n8n

Version

• 1.123.0
• 1.123.1
• 1.123.2
• 1.123.3
• 1.123.4
• 1.123.5
• 1.123.6
• 1.123.7
• 1.123.8
• 1.123.9
• 1.123.10
• 1.123.11
• 1.123.12
• 1.123.13
• 1.123.14
• 1.123.15
• 1.123.16
• 1.123.17
• 1.123.18
• 1.123.19
• 1.123.20
• 1.123.21
• 1.123.22
• 1.123.23
• 1.123.24
• 1.123.25
• 1.123.26
• 1.123.27
• 1.123.28
• 1.123.29
• 1.123.30
• 1.123.31
• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6
• 2.7
• 2.8
• 2.9
• 2.10
• 2.11
• 2.12
• 2.13
• 2.14
• 2.15
• 2.16
• 2.17
• 2.17.0
• 2.17.1
• 2.17.2
• 2.17.3
• 2.18.0

Website

• Product: https://github.com/n8n-io/n8n/

CPE 2.3info

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Once again VulDB remains the best source for vulnerability data.

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