CVE-2026-42861: Flowise: Mass Assignment in Variable Update Endpoint Allows Cross-Workspace Resource Reassignment

Synopsis

A mass assignment vulnerability exists in the variable update endpoint of Flowise, the drag-and-drop LLM flow builder by FlowiseAI. The endpoint is reachable over the network and requires only a low-privilege authenticated account, with no victim interaction needed; an attacker exploits it by sending crafted update requests that include server-controlled fields such as workspaceId, createdDate, and updatedDate. Successful exploitation lets the attacker reassign variables to arbitrary workspaces, breaking tenant isolation in multi-workspace deployments. A fix was shipped in Flowise 3.1.2, and a patched-image rebuild at that version is available on HarborGuard for environments running an affected version.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The vulnerable endpoint is exposed over the network, so the attacker must be able to reach the Flowise service via HTTP/HTTPS.

• AuthenticationRequired

  Any low-privilege authenticated account is sufficient; no elevated or administrative role is needed to send the crafted update request.

• Victim interactionNot required

  The attacker acts entirely on their own by sending a crafted API request; no user needs to click a link or take any other action.

• Attack complexityDetail

  Attack complexity is rated High, meaning the attacker may need to account for environmental factors or specific conditions such as knowing a target workspaceId, though no race condition is explicitly required.

Blast Radius

• Reads variable values stored in the target workspace, which may include API keys, credentials, or other sensitive configuration data injected into LLM flows.
• Reassigns variables from one tenant workspace to another, directly corrupting the resource ownership model and breaking tenant isolation.
• Tampers with server-controlled metadata fields (workspaceId, createdDate, updatedDate), undermining audit trails and access control assumptions that downstream logic depends on.