Vulnerability Report

CVE-2026-40933

Title: Unsafe serialization of stdio commands leads to RCE.

Arbitrary File Access

Proof Of Concept

No public PoC currently indexed for CVE-2026-40933.

CWE Category CWE-78

Published Date Apr 21, 2026

Modified Date Apr 23, 2026

Exploit Status Not Found

Score 9.9 CVSS v3.1

Exploit Probability (EPSS)

13.36%

Vulnerability Summary

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.

Impacted Vendors

flowiseai 1

Reference Links

https://github.com/FlowiseAI/Flowise/security/advisories/GHSA-c9gw-hvqq-f33r https://www.ox.security/blog/mcp-supply-chain-advisory-rce-vulnerabilities-across-the-ai-ecosystem https://www.ox.security/blog/the-mother-of-all-ai-supply-chains-critical-systemic-vulnerability-at-the-core-of-the-mcp

CVSS v3.1

Source Entity [email protected]

Severity CRITICAL

9.9

Attack Vector

NETWORK

Complexity

LOW

Privileges

N/A

Interaction

NONE

Confidentiality

N/A

Integrity

N/A

Availability

N/A

Scope

CHANGED

RAW VECTOR CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Associated Attack Patterns (CAPEC)

Total: Patterns