IBM Langflow OSS EUVD-2026-26447

An attacker must possess valid authentication credentials to log into the Langflow OSS instance (PR:L). No additional configuration, special features, or non-default settings are required - the vulnerability affects all authenticated users against default deployments. The vulnerability is only exploitable in multi-user environments where multiple user accounts exist on the same Langflow instance; single-user installations have no separate user data to target. Additionally, the attacker must have network access to the Langflow API endpoints, which are typically exposed on the application's HTTP/HTTPS port.

CVSS 6.5 (High) with PR:L/AC:L/AV:N indicates moderate real-world risk. The CVSS vector confirms authentication is required (PR:L), but the attack is straightforward once authenticated (AC:L). Exploitation is non-interactive (UI:N) and remote (AV:N), with impact limited to confidentiality (C:H) but no integrity or availability impact from unauthorized reads. However, the vulnerability also permits deletion of another user's vertex build data, which constitutes a confidentiality and potential availability concern in multi-tenant deployments. No active exploitation (KEV status not provided), POC availability not confirmed, but the simplicity of the bypass (direct parameter manipulation) suggests low exploitation friction once the vulnerability is known. This is a real priority in environments with sensitive data sharing between users or where vertex build state is critical to operations, but lower priority in single-user or air-gapped deployments.

An authenticated user of a Langflow OSS instance observes the flow_id pattern in their own flow URLs. They manually craft API requests using different flow_id values to enumerate other users' flows, read their transaction logs containing sensitive data, and delete critical vertex build state to disrupt their workflows. The attack requires only standard HTTP client tools and valid user credentials, taking minutes to execute once the vulnerability is discovered.