Langflow OSS Authorization Bypass Through User-Controlled Key

Overview

IBM Langflow OSS 1.0.0 through 1.12.4 contains three message endpoints that perform no ownership verification. Any authenticated user can bulk-delete another user's messages, overwrite message content to inject malicious prompts, or hijack an entire conversation session by reassigning its session ID.

Affected

• langflow_oss >= 1.0.0 <= 1.12.4

Remediation

IBM strongly recommends addressing the vulnerability now by upgrading Langflow OSS to version 1.12.5. https://pypi.org/project/langflow/1.12.5/

For Langflow OSS versions 1.0.0 - 1.12.4, follow the Prepare to upgrade instructions and release-specific configuration changes https://docs.langflow.org/release-notes , including backing up your existing installation, then follow the Langflow OSS installation instructions https://docs.langflow.org/get-started-installation to install version 1.12.5 and test your flows. For deployments using MCP stdio, also apply the configuration controls in Workarounds and Mitigations.

This bulletin also discloses fixes delivered in prior releases: CVE-2026-107366 was fixed in version 1.9.0; CVE-2026-18894 was fixed in version 1.11.2; and CVE-2026-77817 was fixed in version 1.11.5. Version 1.12.5 includes these fixes.

Workarounds

IBM strongly recommends applying the following configuration controls to deployments using MCP stdio in addition to upgrading Langflow OSS to version 1.12.5. These controls do not replace the upgrade.

Set LANGFLOW_MCP_SERVER_INTERPRETER_HARDENING=true to reject direct shell-script execution, and set LANGFLOW_CUSTOM_COMPONENT_ADMIN_ONLY=true to block non-admin MCP stdio access. Restart the Langflow service after updating its environment configuration. These restrictions can require changes to existing MCP server launch configurations and limit which users can use MCP stdio.

For public workflows, retain the default restriction on custom components. Explicitly enabling LANGFLOW_ALLOW_PUBLIC_CUSTOM_COMPONENTS permits custom component execution and changes the default protection described for CVE-2026-18894.

For CVE-2026-77817, upgrading prevents the identified secret disclosure in new flow and project exports. Revoke or rotate any credentials exposed in previously exported files; upgrading does not remove secrets from copies already exported.