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FlowiseApplication · Flowiseai

CVE-2026-40933

CRITICAL · 9.9 CVSS v3.1 Published 2026-04-21
Fix available
A fix is available. Upgrade to 3.1.0 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Flowise versions prior to 3.1.0 contain a command injection vulnerability in the MCP (Model Context Protocol) adapter. Authenticated users can bypass existing input sanitization (validateCommandInjection, validateArgsForLocalFileAccess, and safe command allowlists) by appending code execution arguments to permitted commands like 'npx -c <malicious_command>'. This allows arbitrary OS command execution on the underlying host through the Custom MCP configuration at /canvas.

MitigationUpgrade to Flowise version 3.1.0 or later, which addresses the unsafe stdio command serialization and fixes the input sanitization bypass in the MCP adapter.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FlowiseApplication
Affected:< 3.1.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Flowise installation and version
    Locate the Flowise installation directory and check the version in package.json, or run 'npm list flowise' or check the running service version endpoint if available
    Affected if The installed version is prior to 3.1.0
  2. Confirm MCP adapter is enabled
    Check Flowise configuration files or environment variables for MCP-related settings, or inspect the /canvas endpoint for MCP-related routes
    Affected if MCP adapter is enabled or configurable in the environment
  3. Inspect Custom MCP configuration at /canvas
    Review the MCP configuration settings in the Flowise database or configuration files for any custom MCP server definitions, particularly those using npx commands
    Affected if Custom MCP configurations exist that use shell commands like npx with user-controlled arguments
  4. Check for recent unauthorized access
    Review Flowise access logs for requests to /canvas involving MCP configuration changes, particularly those containing suspicious command patterns
    Affected if There are log entries showing MCP configuration changes with potentially malicious command strings

You are affected if Flowise version is less than 3.1.0 AND the MCP adapter is enabled or configurable, allowing an authenticated attacker to inject commands through Custom MCP settings at /canvas.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 3.1.0 or later
Fixed in 3.1.0
Interim mitigation

Upgrade to Flowise version 3.1.0 or later, which addresses the unsafe stdio command serialization and fixes the input sanitization bypass in the MCP adapter.

Recommended fix High confidence

Flowise 3.1.0 or later

  1. 1. Back up your current Flowise installation and any custom configurations
  2. 2. Stop the Flowise service
  3. 3. Upgrade Flowise to version 3.1.0 or later using your package manager (npm, yarn, or docker) - for npm: npm install flowise@latest or specific version npm install [email protected]
  4. 4. Restart the Flowise service
  5. 5. Verify the upgrade was successful by checking the version at http://localhost:3000 or via CLI: npx flowise@latest --version
  6. 6. Test that the Custom MCP functionality works correctly in the /canvas interface after the upgrade
Caveat Review the Flowise 3.1.0 release notes for any breaking changes between your current version and 3.1.0 before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Flowise Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-40933 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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