Overview
CVE-2026-40933 is a critical command injection vulnerability in Flowise, the drag-and-drop UI platform for building customized LLM flows. The vulnerability exists in the Model Context Protocol (MCP) adapter’s unsafe serialization of stdio commands, allowing authenticated attackers to execute arbitrary commands on the underlying operating system.
Root Cause
MCP’s stdio transport is designed to launch local server processes and communicate with them through standard input and output streams, allowing AI agents to interact with files, Git repositories, databases, browsers, and local credentials. The issue stems from Flowise allowing users to configure MCP stdio servers containing arbitrary commands — because those commands are ultimately executed by the underlying OS, an attacker can achieve RCE with the privileges of the Flowise process.
Exploitation Mechanics
Two distinct attack paths exist:
- Direct configuration abuse: Exploitation occurs if an authenticated user adds a new MCP with a malicious stdio configuration.
- One-click chatflow import: An attacker can fully compromise a server by convincing an authorized user to import a crafted chatflow. Import alone is enough to trigger arbitrary server-side code execution — before any save or run action.
Bypass of initial patch: Flowise added flag validation to block risky flags such as -y, -c, --yes, --eval, and similar options when used with allowlisted commands. However, the official patch relies on input validation that is trivially bypassed and fails to address the root cause.
Impact
An authenticated attacker can achieve full remote code execution on the Flowise server, potentially compromising the entire AI/ML infrastructure and any connected systems.
Patch & Remediation
- Upgrade to Flowise 3.1.0 (both
flowiseandflowise-componentsnpm packages) - Do not treat MCP stdio as harmless configuration — treat any user-configurable stdio MCP server as a process execution surface
- Do not rely on input sanitization as the primary control for stdio command paths
- Restrict who can add/import MCP configurations or chatflows in multi-user Flowise deployments
- Consider network-level isolation of Flowise instances from sensitive internal systems
Broader Context
CVE-2026-40933 and a related vulnerability in Upsonic (CVE-2026-30625) connect to a broader MCP supply-chain pattern: products allowed users to configure MCP stdio servers, and that configuration could reach OS-level process execution paths. This is a systemic design risk across the agentic AI ecosystem — any platform that exposes MCP stdio configuration to users without sandboxing is carrying the same architectural exposure regardless of whether a CVE has been assigned yet.
