Langflow Unrestricted File Upload Vulnerability (CVE-2026-6596)

A critical security vulnerability, identified as CVE-2026-6596, has been discovered in langflow-ai langflow, affecting versions up to 1.1.0. The vulnerability resides within the create_upload_file function of the src/backend/base/Langflow/api/v1/endpoints.py file, specifically in the API Endpoint component. This flaw allows for unrestricted file uploads, potentially enabling attackers to upload and execute malicious files on the server. The vulnerability is remotely exploitable and an exploit has been publicly released, increasing the risk of widespread exploitation. The vendor was notified, but did not respond.

Attack Chain

1. An attacker identifies a Langflow instance running a vulnerable version (<= 1.1.0).
2. The attacker sends a crafted HTTP POST request to the create_upload_file API endpoint.
3. The request includes a malicious file disguised with a permissible extension or without proper validation.
4. The create_upload_file function fails to adequately validate the uploaded file type or size.
5. The malicious file is written to the server’s file system in an accessible location.
6. The attacker crafts a second request to execute the uploaded malicious file. This could involve accessing the file directly via a web browser or triggering its execution through other server-side processes.
7. Successful execution of the file grants the attacker arbitrary code execution on the server.
8. The attacker leverages code execution to compromise the system, potentially leading to data exfiltration, service disruption, or further lateral movement within the network.

Impact

Successful exploitation of this vulnerability could allow an attacker to gain complete control over the affected Langflow instance. This could lead to the compromise of sensitive data, disruption of services, and potential further attacks on other systems within the network. Given the ease of exploitation and the availability of a public exploit, organizations using vulnerable versions of Langflow are at significant risk. The impact would depend on the deployment and data handled by the Langflow installation.

Recommendation

• Upgrade Langflow to a version higher than 1.1.0 to patch CVE-2026-6596.
• Implement the Sigma rule Detect Suspicious File Uploads to Langflow API to detect exploitation attempts targeting the create_upload_file endpoint.
• Monitor web server logs for suspicious POST requests to the /api/v1/upload endpoint, as this is the likely path for exploitation.