n8n: Session token leak via Dynamic Credentials endpoints

Summary

n8n versions before 2.39.6 and 2.40.0 before 2.40.1 leak the caller's raw session token from the Dynamic Credentials authorize and revoke endpoints to a configured credential resolver. A user who can register a resolver (CWE-863) can set a fallback resolver to an attacker-controlled endpoint and capture a collaborator's or the owner's session token during the "Connect your account" flow. The attacker can then read credentials they have no access to. The attack requires high privileges and user interaction, and is not reachable without a logged-in account.

Affected

• n8n before 2.39.6 (all versions below 2.39.6)
• n8n 2.40.0 before 2.40.1
• Versions 1.x: Unknown. The GitHub advisory lists only the 2.x branches; check the advisory before assuming either way.
• Cloud instances: patched automatically according to the vendor community post.

Fixed in

• Upgrade to n8n 2.39.6 or later on the 2.39 branch
• Upgrade to n8n 2.40.1 or later on the 2.40 branch

Workaround

• Restrict instance access to fully trusted users only
• Disable the Dynamic Credentials module if it is not required
• Audit and revoke custom global roles with the credentialResolver:create scope, limiting it to fully trusted administrators
• Review registered credential resolvers and remove unknown ones or ones pointing to unexpected URLs
• Rotate session tokens and credentials for users who used "Connect your account" on shared workflows with an externally registered resolver
• These measures reduce the risk but do not fully remediate it

Exploitation

• No evidence of exploitation in the wild found; CISA SSVC: Exploitation none, Automatable no, Technical Impact total
• No public proof of concept found
• EPSS score very low (0.00239, aggregator data)

Our recommendation

• Identify all self-hosted n8n instances and their versions
• Upgrade self-hosted instances to 2.39.6 or 2.40.1 (or later) as a priority
• Until patching is done, apply the workarounds above
• Review users, API keys and OAuth clients on internet-reachable instances, look for unrecognised executions, and rotate credentials stored in n8n
• Check the GitHub advisory feed directly, as related advisories from the same batch may not be in the CVE database

Public exploits iAttack code is publicly available (PoC on GitHub, Metasploit or Exploit-DB).

PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.

Research sources

• GitHub Security Advisory GHSA-rx55-8qhx-4hwx github.com
• VulnCheck advisory: n8n session token leak via Dynamic Credentials www.vulncheck.com
• OSV: CVE-2026-103259 osv.dev
• n8n community security update (16 September 2026) community.n8n.io
• n8n fix commit ac411127314921aaf82b7b97d76eeaa2703b708c github.com

Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 11:41.