CVE-2026-21858 is a critical security vulnerability found in the open-source workflow automation platform n8n, affecting all versions prior to 1.121.0. The root cause is improper input validation (CWE-20) in certain form-based workflows, which allows an unauthenticated remote attacker to execute crafted inputs that access files on the underlying server. This flaw essentially enables attackers to bypass authentication and retrieve sensitive files, potentially including configuration files, credentials, or other confidential data stored on the system. The vulnerability can also facilitate further compromise depending on how the workflows are deployed and the nature of the data processed. The CVSS v3.1 base score is 10.0, reflecting the highest severity due to network attack vector, no required privileges, no user interaction, and complete impact on confidentiality and integrity, though availability is not affected. The vulnerability was publicly disclosed on January 7, 2026, and fixed in n8n version 1.121.0. No public exploits have been reported yet, but the critical nature and ease of exploitation make it a significant threat. Organizations using n8n should prioritize upgrading to the patched version and audit their workflow configurations to ensure no vulnerable workflows remain active. Additionally, limiting network exposure of n8n instances and implementing strict access controls can reduce risk.

For European organizations, this vulnerability poses a severe risk of data breach and unauthorized access to sensitive information managed within n8n workflows. Given n8n’s role in automating business processes, exposure of internal files could lead to leakage of intellectual property, customer data, or credentials, potentially enabling lateral movement or further attacks within the network. Organizations in sectors such as finance, healthcare, manufacturing, and government, which often rely on automation platforms and handle sensitive data, are particularly vulnerable. The critical severity and unauthenticated remote exploitability mean that attackers can compromise systems without insider access or user interaction, increasing the likelihood of rapid exploitation. This could disrupt business operations, damage reputation, and incur regulatory penalties under GDPR if personal data is exposed. The impact is magnified in environments where n8n is integrated with other critical systems or cloud services, as attackers could leverage the initial access to escalate privileges or pivot to other assets.

1. Immediately upgrade all n8n instances to version 1.121.0 or later to apply the official patch addressing CVE-2026-21858. 2. Conduct a thorough audit of all existing workflows, especially those involving form inputs, to identify and disable any potentially vulnerable workflows until patched. 3. Restrict network access to n8n instances by implementing firewall rules, VPNs, or zero-trust network segmentation to limit exposure to trusted users and systems only. 4. Implement strong authentication and authorization controls on n8n, even though the vulnerability allows unauthenticated access, to reduce attack surface and monitor for suspicious activity. 5. Monitor logs and network traffic for unusual file access patterns or attempts to exploit form inputs. 6. Educate development and operations teams about secure workflow design and input validation best practices to prevent similar issues. 7. Consider deploying web application firewalls (WAFs) with custom rules to detect and block malicious payloads targeting form inputs. 8. Regularly review and update incident response plans to include scenarios involving workflow automation platform compromises.