Vulnerability Description
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.
CVSS Score
CRITICAL
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Flowiseai | Flowise | < 3.1.0 |
Related Weaknesses (CWE)
References
- https://github.com/FlowiseAI/Flowise/security/advisories/GHSA-c9gw-hvqq-f33rExploitVendor Advisory
- https://www.ox.security/blog/mcp-supply-chain-advisory-rce-vulnerabilities-acrosPress/Media CoverageThird Party Advisory
- https://www.ox.security/blog/the-mother-of-all-ai-supply-chains-critical-systemiPress/Media CoverageThird Party Advisory
- https://github.com/FlowiseAI/Flowise/security/advisories/GHSA-c9gw-hvqq-f33rExploitVendor Advisory
FAQ
What is CVE-2026-40933?
CVE-2026-40933 is a vulnerability with a CVSS score of 9.9 (CRITICAL). 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...
How severe is CVE-2026-40933?
CVE-2026-40933 has been rated CRITICAL with a CVSS base score of 9.9/10. This is considered a critical vulnerability requiring immediate attention.
Is there a patch for CVE-2026-40933?
Check the references section above for vendor advisories and patch information. Affected products include: Flowiseai Flowise.