CVE-2026-42861 is a critical mass assignment flaw (CVSS 9.6) in Flowise, the drag and drop LLM flow builder. Authenticated users can change server controlled fields on a variable, including its workspace, which can break tenant isolation. The advisory lists versions up to 3.1.1 as affected and 3.1.2 as the fix.
What's affected
The advisory says versions up to and including 3.1.1 are affected, and 3.1.2 is patched. The NVD record words it as before 3.1.2.
The flaw matters most for multi workspace deployments, where several teams or customers share one Flowise server. A single user installation has less to lose, though the upgrade is still sensible.
How to check if you're exposed
npm ls flowise
For Docker, read the image tag in your compose file or run docker image ls on the host. If you use the hosted Flowise service, ask the provider about their version.
Then look at how you use workspaces. If several tenants share one instance, review recent changes to variables and check that each variable still sits in the workspace you expect. The endpoint involved is the variable update call, PUT on the variables API.
What to do now
- Upgrade Flowise to 3.1.2 or later.
- Review variables in each workspace, and check any that moved or that you do not recognise.
- Rotate secrets stored in variables if you cannot rule out tampering.
- Limit who holds accounts on shared instances, and remove unused ones.
- Check the earlier fix in 3.1.0 for SSRF is also in place by being on 3.1.2 or later.
Why it matters
The record lists CWE-284 (improper access control), CWE-639 (authorization bypass through a user controlled key) and CWE-915 (improperly controlled modification of dynamically determined object attributes). Together they describe mass assignment: the endpoint copies whatever fields the request body contains onto the stored object, including fields that only the server should set.
Changing the workspace identifier moves a resource into another tenant, and in the other direction it can pull in or expose resources. That undermines the boundary a multi tenant system promises. The KEV flag is false.
Quick check
What is mass assignment?
It is when an API binds every field in a request to an internal object without an allow list, so a caller can set fields they should not control.
Sources
Last reviewed: 19 October 2026.
