CVE-2026-42861: Flowise: mass assignment breaks multi-tenant isolation

### Summary A Mass Assignment vulnerability exists in the variable update endpoint of FlowiseAI. The endpoint allows authenticated users to modify server-controlled properties such as workspaceId, createdDate, and updatedDate when updating a variable resource. Due to missing server-side validation and authorization checks, an attacker can manipulate the workspaceId field and reassign variables to arbitrary workspaces. This behavior may break tenant isolation in multi-workspace environments. ### Details The endpoint responsible for updating variables: **PUT /api/v1/variables/{variableId}** accepts a JSON request body containing the variable definition. However, the backend does not restrict which attributes can be modified by the client. As a result, user-controlled request bodies can include internal properties that should normally be controlled exclusively by the server. Server-controlled fields that can be manipulated include: - workspaceId - createdDate - updatedDate These fields appear to be directly mapped to the database entity without strict input validation or authorization checks. For example, the following request body was accepted by the server: ```json { "name": "aaa", "value": "bbbe", "type": "static", "createdDate": "2016-03-06T17:59:30.000Z", "updatedDate": "2016-03-06T18:00:17.000Z", "workspaceId": "11111111-2222-3333-4444-555555555555" } ``` The server accepted the attacker-controlled workspaceId and metadata fields and persisted them. ### PoC **Request** ```http PUT /api/v1/variables/<VARIABLE_ID> Content-Type: application/json { "name": "aaa", "value": "bbbe", "type": "static", "createdDate": "2016-03-06T17:59:30.000Z", "updatedDate": "2016-03-06T18:00:17.000Z", "workspaceId": "11111111-2222-3333-4444-555555555555" } ``` **Response** ```json { "id": "0a2b9f61-4a97-4ff8-b80d-00275ed18674", "name": "aaa", "value": "bbbe", "type": "static", "createdDate": "2016-03-06T17:59:30.000Z", "updatedDate": "2026-03-06T18:05:17.000Z", "workspaceId": "11111111-2222-3333-4444-555555555555" } ``` This confirms that the backend accepts and persists attacker-controlled internal properties. ### Impact This vulnerability allows authenticated users to manipulate internal attributes of variable resources. Possible impacts include: 1. Cross-workspace reassignment of variables (workspaceId) 2. Unauthorized modification of metadata (createdDate, updatedDate) 3. Potential tenant isolation bypass in multi-workspace deployments In multi-tenant environments, this may allow an attacker to move variables between workspaces without authorization.

A legitimate but malicious user in a shared Flowise deployment authenticates with their own workspace credentials. They identify target workspace UUIDs through error messages, enumeration, or brute-force of the UUID space. The attacker selects a variable they own and sends a PUT /api/v1/variables/{id} request with the victim's workspaceId injected into the JSON body alongside normal fields. The backend persists the record with the attacker-controlled workspaceId without validation. Depending on application logic governing workspace-level reads, the attacker can now access or contaminate variables in the victim workspace — harvesting LLM API keys, injecting malicious system prompt values, or altering model endpoint configurations to redirect AI agent traffic. Forged createdDate and updatedDate fields are used to disguise the tampering in audit logs.