CVE-2026-5027 is a path traversal vulnerability in Langflow's 'POST /api/v2/files' endpoint that fails to sanitize the 'filename' parameter in multipart form data. This allows unauthenticated attackers to write files to arbitrary filesystem locations using '../' sequences. Due to Langflow's default unauthenticated auto-login feature, attackers can obtain valid session tokens with a single request and exploit this flaw to achieve remote code execution. Exploitation attempts have been observed in the wild, with attackers successfully dropping test files on victim systems. The vulnerability was disclosed publicly on March 27, 2026, by Tenable after failed disclosure attempts. The attack surface is broad, with thousands of internet-accessible Langflow instances.

Successful exploitation allows unauthenticated remote attackers to write arbitrary files anywhere on the system, leading to remote code execution. This compromises the confidentiality, integrity, and availability of affected systems. Because Langflow permits unauthenticated auto-login, attackers do not need credentials to exploit the vulnerability, increasing the risk and ease of attack. Active exploitation attempts have been observed, indicating real-world threat activity.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, restrict internet exposure of Langflow instances and monitor for suspicious activity targeting the 'POST /api/v2/files' endpoint. Disable unauthenticated auto-login if possible to reduce attack surface. Follow updates from Langflow and security advisories for official patches or mitigations.