What is CVE-2026-40933?

CVE-2026-40933 is a critical-severity vulnerability in Flowiseai Flowise, classified under OS Command Injection. CVSS score: 9.9/10. Published 2026-04-21.

How severe is CVE-2026-40933?

Critical severity. CVSS v3 base score is 9.9 out of 10.

RCE in Flowiseai Flowise

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.

Vulnerability class: Command Injection (OS Command Injection)

Published 2026-04-21 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.9 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.013 (69.6th percentile), scored 2026-10-19.

Low probability of exploitation in the next 30 days, but still tracked. 70th percentile — 69.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.120 · newest: 0.013 · change: -0.107

Affected products

Flowiseai Flowise — versions < 3.1.0
Flowiseai Flowise-Components — versions < 3.1.0

Weakness classification (CWE)

CWE-78 — OS Command Injection

References

github.com/FlowiseAI/Flowise/security/advisories/GHSA-c9gw-hvqq-f33r (Exploit, Vendor Advisory)
www.ox.security/blog/mcp-supply-chain-advisory-rce-vulnerabilities-across-the-a… (Third Party Advisory, Press/Media Coverage)
www.ox.security/blog/the-mother-of-all-ai-supply-chains-critical-systemic-vulne… (Third Party Advisory, Press/Media Coverage)

Frequently asked questions

What is CVE-2026-40933?: CVE-2026-40933 is a critical-severity vulnerability in Flowiseai Flowise, classified under OS Command Injection. CVSS score: 9.9/10. Published 2026-04-21.
How severe is CVE-2026-40933?: Critical severity. CVSS v3 base score is 9.9 out of 10.