Active exploitation of Langflow bug CVE-2026-5027

An unpatched path-traversal vulnerability in Langflow, tracked as CVE-2026-5027 (CVSS 8.8), is being actively exploited to write files to arbitrary locations and enable unauthenticated remote code execution. Tenable discovered the flaw and published technical details on March 27, 2026, after three unsuccessful contact attempts with project maintainers in January and February.

The bug is in the POST /api/v2/files endpoint, which fails to sanitize the filename parameter in multipart form data. Attackers can include path-traversal sequences such as “../” to place files outside intended directories and into locations that can be used to run code.

Researchers at VulnCheck reported observing active exploitation in the wild. Activity seen so far consists of test file writes on compromised hosts, while the underlying ability to write to arbitrary paths can be adapted to drop web shells or other executable payloads.

Caitlin Condon, vice president of security research at VulnCheck, wrote on LinkedIn that Langflow’s default configuration enables unauthenticated auto-login. A single unauthenticated request can produce a valid session token and allow an attacker to access the vulnerable endpoint.

Internet scan data from Censys shows roughly 7,000 Langflow instances are reachable from the public internet, with most located in North America. The number of exposed deployments increases the surface available to opportunistic actors scanning for vulnerable instances.

The activity follows multiple other vulnerabilities affecting Langflow this year, including CVE-2026-0770, CVE-2026-33017, CVE-2026-21445 and CVE-2025-34291. Security teams previously linked CVE-2025-34291 to operations by the Iranian state-linked group MuddyWater.

Tenable and other vendors published technical advisories and exploit details after disclosure. Administrators of exposed Langflow deployments are advised to follow vendor recommendations, restrict public access to management endpoints, and review logs for unexpected file writes and session creation.

Tenable’s advisory states: “the POST /api/v2/files endpoint does not sanitize the ‘filename’ parameter from the multipart form data, allowing an attacker to write files to arbitrary locations on the filesystem using path traversal sequences (“../”).”