CVE-2026-42230: 
NixOS vulnerability analysis and mitigation

CVE-2026-42230 is an open redirect vulnerability in n8n, an open-source workflow automation platform, affecting the MCP OAuth consent flow. The /mcp-oauth/register endpoint accepts OAuth client registrations without authentication, allowing arbitrary redirect_uri values to be registered; when a user denies the consent dialog, the handleDeny handler redirects them to the unvalidated URI. Affected versions include all n8n releases before 1.123.32, 2.0.0–2.17.3, and 2.18.0. The advisory was first published on April 22, 2026, and disclosed publicly on April 29, 2026. It carries a CVSS v4.0 base score of 5.1 (Medium) and a CVSS v3.1 score of 6.1 (Medium) (GitHub Advisory, n8n Security Advisory).

The root cause is CWE-601 (URL Redirection to Untrusted Site / Open Redirect): the /mcp-oauth/register endpoint lacks authentication, permitting any unauthenticated actor to register an OAuth client with an arbitrary redirect_uri. The handleDeny handler in the MCP OAuth consent flow then blindly redirects users to this registered URI upon denial of the consent dialog, without performing any allowlist or domain validation. Exploitation requires no privileges and only low attack complexity, but does require user interaction — specifically, the victim must click "Deny" on the crafted consent page. The reporter credited for discovery is ori-ron (GitHub Advisory, n8n Security Advisory).

Successful exploitation enables an attacker to silently redirect victims to an attacker-controlled external site, facilitating phishing, credential harvesting, or malware delivery. The confidentiality impact is low (limited information disclosure via the redirect itself), and there is no direct integrity or availability impact on the n8n system. However, the subsequent system (the victim's browser/session) may be exposed to further compromise depending on the attacker's landing page (GitHub Advisory).

No public exploit code or in-the-wild exploitation has been reported for CVE-2026-42230 as of the available data. The EPSS score is approximately 0.056% (18th percentile), indicating a low near-term exploitation probability. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. No threat actor attribution has been identified (GitHub Advisory).

1. Reconnaissance: Identify internet-accessible n8n instances running versions prior to 1.123.32, 2.17.4, or 2.18.1 using tools like Shodan or Censys, searching for n8n login pages or MCP OAuth endpoints.
2. Register malicious OAuth client: Send an unauthenticated HTTP POST request to the /mcp-oauth/register endpoint of the target n8n instance, supplying an attacker-controlled URL as the redirect_uri value (e.g., https://attacker.example.com/phish).
3. Craft phishing link: Construct a URL pointing to the n8n MCP OAuth consent page that references the newly registered client ID, so the consent dialog is presented to the victim.
4. Deliver phishing link: Send the crafted link to the target victim via email, messaging, or other social engineering channels.
5. Trigger redirect: When the victim visits the link and clicks "Deny" on the MCP OAuth consent dialog, the handleDeny handler redirects them to the attacker-controlled redirect_uri without validation.
6. Achieve objective: The victim lands on the attacker's site, where credential phishing, session token theft, or malware delivery can be attempted (GitHub Advisory, n8n Security Advisory).

• Network: Unauthenticated POST requests to /mcp-oauth/register from external or unexpected IP addresses; HTTP redirects (3xx responses) from the n8n server to external/unknown domains following requests to the MCP OAuth consent denial endpoint.
• Logs: n8n access logs showing repeated unauthenticated calls to /mcp-oauth/register with varying redirect_uri values; log entries for handleDeny redirects to non-whitelisted external domains.
• Application: Presence of OAuth client registrations in the n8n database with redirect_uri values pointing to external or suspicious domains not associated with legitimate integrations.

Upgrade n8n to version 1.123.32, 2.17.4, or 2.18.1 (or later), which contain the fix for this vulnerability. If immediate upgrade is not possible, restrict network access to the n8n instance so that untrusted users cannot reach the MCP OAuth endpoints, and limit access to fully trusted users only. These workarounds do not fully remediate the risk and should be treated as short-term measures only (GitHub Advisory, n8n Security Advisory).

The vulnerability was mentioned in The Hacker News' weekly recap alongside other notable security issues, indicating moderate community awareness (The Hacker News). Checkmarx published a post covering related n8n vulnerabilities from the same disclosure period, suggesting broader researcher interest in n8n's security posture (Checkmarx). No significant vendor statements beyond the official advisory or notable individual researcher commentary specific to this CVE have been identified.