CVE-2026-103259: n8n Session Token Leakage Vulnerability

CVE-2026-103259 Overview

CVE-2026-103259 is a session token leakage vulnerability in n8n, the workflow automation platform. The flaw affects the Dynamic Credentials authorize and revoke endpoints in n8n versions before 2.39.6 and 2.40.0 before 2.40.1. An attacker with resolver registration capability can register a fallback resolver pointing to an attacker-controlled endpoint. During the account connection flow, collaborators' session tokens are transmitted to that endpoint, enabling the attacker to capture valid tokens and access credentials belonging to other users. The weakness is classified under CWE-863: Incorrect Authorization.

Critical Impact

Attackers who already hold resolver registration privileges can hijack collaborator sessions and gain unauthorized access to stored credentials used by automation workflows.

Affected Products

• n8n versions before 2.39.6
• n8n versions 2.40.0 before 2.40.1
• Dynamic Credentials authorize and revoke endpoints

Discovery Timeline

• 2026-10-01 - CVE-2026-103259 published to NVD
• 2026-10-01 - Last updated in NVD database

Technical Details for CVE-2026-103259

Vulnerability Analysis

n8n supports Dynamic Credentials, which allow workflows to resolve authentication material at runtime through registered resolver endpoints. The authorize and revoke endpoints handle the OAuth-style account connection flow for these credentials. During this flow, n8n forwards request context, including session tokens belonging to the collaborator initiating the action, to the configured resolver.

The vulnerability stems from insufficient authorization checks when a fallback resolver is registered. An attacker who can register a resolver can set the fallback target to an endpoint under their control. When a legitimate collaborator triggers the authorize or revoke flow, their session token is leaked to the attacker-controlled URL. The attacker can then replay the captured token to impersonate the collaborator and access any credentials the victim is authorized to use.

Root Cause

The root cause is improper authorization enforcement [CWE-863] in the Dynamic Credentials pipeline. n8n permits resolver registration without validating that the registered fallback destination is trusted, and it forwards session tokens to that destination without scope restriction. The resolver registration path and the token-forwarding behavior do not jointly enforce that the destination is permitted to receive authenticated session material.

Attack Vector

Exploitation requires high privileges (resolver registration capability) and user interaction from a victim collaborator who initiates an account connection or revocation. The attacker performs the following steps:

1. Register a Dynamic Credentials resolver with a fallback endpoint pointing to attacker-controlled infrastructure.
2. Wait for or socially engineer a collaborator into initiating the authorize or revoke flow for a Dynamic Credential.
3. Capture the collaborator's session token as it is transmitted to the fallback endpoint.
4. Replay the captured token against the n8n API to access credentials and workflows available to the victim.

No verified public exploit code is available. See the GitHub Security Advisory GHSA-rx55-8qhx-4hwx and the VulnCheck Advisory on n8n for additional technical context.

Detection Methods for CVE-2026-103259

Indicators of Compromise

• Dynamic Credentials resolver registrations whose fallback URL points to external, unrecognized, or recently registered domains.
• Outbound requests from n8n to non-approved hosts containing Authorization headers or session cookies during authorize or revoke operations.
• Session tokens observed being used from IP addresses or user agents that differ from the collaborator's typical pattern.

Detection Strategies

• Audit the n8n configuration and database for all registered Dynamic Credentials resolvers and validate that each fallback destination is on an allowlist.
• Inspect reverse proxy and egress logs for POST or GET requests from n8n to the authorize and revoke resolver endpoints and correlate the destination against trusted integrations.
• Correlate session token usage with originating client fingerprints to identify replay from unexpected sources.

Monitoring Recommendations

• Enable egress network monitoring on the n8n host and alert on connections to domains not present in an approved integration list.
• Log and review all administrative actions that create or modify Dynamic Credentials resolvers.
• Monitor authentication events for session token reuse across disparate IPs or geographies within short time windows.

How to Mitigate CVE-2026-103259

Immediate Actions Required

• Upgrade n8n to version 2.39.6 or 2.40.1 or later, depending on the deployed branch.
• Review existing Dynamic Credentials resolver registrations and remove any whose fallback endpoints are not explicitly trusted.
• Rotate n8n user session tokens and credentials that may have been exposed through the vulnerable endpoints.

Patch Information

The maintainers resolved the issue in n8n 2.39.6 and 2.40.1. Refer to the GitHub Security Advisory GHSA-rx55-8qhx-4hwx for the authoritative fix details and version matrix.

Workarounds

• Restrict resolver registration capability to a minimal set of trusted administrators until the upgrade is applied.
• Place n8n behind an egress proxy that enforces an allowlist of outbound destinations for the authorize and revoke flows.
• Temporarily disable Dynamic Credentials usage for sensitive accounts until patched versions are deployed.

# Upgrade n8n via npm to a patched release
npm install -g n8n@2.40.1

# Or pin to the 2.39.x patched line
npm install -g n8n@2.39.6

# Verify installed version
n8n --version