Attackers exploit unpatched Langflow flaw for unauthenticated code execution

VulnCheck reports that attackers are actively exploiting an unpatched flaw in Langflow, a popular open-source platform for building AI applications. The bug (CVE-2026-5027, rated 8.8) is a path-traversal weakness: the file-upload endpoint does not clean the supplied filename, so an attacker can use directory-climbing sequences to write files anywhere on the server, a foothold that leads to remote code execution. Tenable, which found it, says the maintainers did not respond after three contact attempts in early 2026, and there is still no official fix. Early exploitation appears to be probing, with attackers writing harmless test files, but that usually precedes heavier attacks.

Check

Identify any internet-facing Langflow instances, confirm the version, and review the server filesystem and web logs for unexpected files written via the /api/v2/files upload endpoint.

Affected

Internet-exposed Langflow deployments where the file-upload endpoint is reachable (CVE-2026-5027). No vendor patch is available yet, and active exploitation is already under way.

Fix

Until a fix ships, take Langflow off the public internet or place it behind authentication and a WAF that blocks path-traversal payloads, and restrict the upload endpoint.