CVE-2026-40933

Flowise is a drag & drop user interface to build a customized large language model flow. Prior to 3.1.0, due to unsafe serialization of stdio commands in the MCP adapter, an authenticated attacker can add an MCP stdio server with an arbitrary command, achieving command execution. The vulnerability lies in a bug in the input sanitization from the “Custom MCP” configuration in http://localhost:3000/canvas - where any user can add a new MCP, when doing so - adding a new MCP using stdio, the user can add any command, even though your code have input sanitization checks such as validateCommandInjection and validateArgsForLocalFileAccess, and a list of predefined specific safe commands - these commands, for example "npx" can be combined with code execution arguments ("-c touch /tmp/pwn") that enable direct code execution on the underlying OS. This vulnerability is fixed in 3.1.0.

• CWE-78

• https://github.com/FlowiseAI/Flowise/security/advisories/GHSA-c9gw-hvqq-f33rExploit, Vendor Advisory
• https://www.ox.security/blog/mcp-supply-chain-advisory-rce-vulnerabilities-across-the-ai-ecosystemPress/Media Coverage, Third Party Advisory
• https://www.ox.security/blog/the-mother-of-all-ai-supply-chains-critical-systemic-vulnerability-at-the-core-of-the-mcpPress/Media Coverage, Third Party Advisory
• https://github.com/FlowiseAI/Flowise/security/advisories/GHSA-c9gw-hvqq-f33rExploit, Vendor Advisory

Published

Apr 21, 2026

Last Modified

Jun 17, 2026

Status

Analyzed