Windmill EUVD-2026-56011

Exploitation requires a valid authenticated session as a workspace member in the target Windmill workspace (confirmed by CVSS PR:L); no administrator account, no privilege escalation, and no special workspace role beyond basic membership is needed. The attacker must have network access to the Windmill API (CVSS AV:N), which is typically exposed over HTTP/HTTPS. The vulnerability is scoped to the update_resource_type endpoint - the attacker must know or enumerate the names of resource types within the workspace, which is generally accessible to all members. Exploitation is bounded by the following limiting factors: only authenticated workspace members can exploit this (unauthenticated users are excluded); impact is limited to integrity of resource type schemas and the availability of dependent workflows - there is no confidentiality breach or code execution path via this endpoint alone; and the attacker is limited to corrupting resource types within workspaces they are a member of, not across the entire Windmill instance.

The vendor-assigned CVSS 3.1 score of 6.5 (AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N) is broadly accurate: network-accessible, low complexity, low-privilege attack with no user interaction required. The provided vector assigns no availability impact, but the description explicitly states that corrupting resource type definitions breaks dependent workflows, which introduces a meaningful availability dimension not reflected in the official score. No EPSS data was supplied, so exploitation probability cannot be quantified. The vulnerability is not listed in CISA KEV and no POC was referenced, indicating no confirmed active exploitation at time of analysis. Real-world risk is highest in multi-tenant or shared-workspace Windmill deployments where workspace members are not uniformly trusted - a malicious insider or compromised low-privilege account can silently corrupt schema definitions, causing cascading workflow failures that may be difficult to attribute. Risk is lower in single-organization deployments with tightly controlled membership. The missing availability signal in the official CVSS is a notable gap.

A disgruntled workspace member - or an attacker who has phished or brute-forced a low-privilege Windmill account - authenticates to the Windmill API and sends a crafted HTTP request to the update_resource_type endpoint with a malformed or empty schema payload, targeting a resource type that critical production workflows depend on. Because the authorization check is absent, the request succeeds silently and overwrites the legitimate schema. Downstream workflows that reference the corrupted resource type then begin failing with schema validation errors, causing operational disruption that is difficult to trace back to the unauthorized schema modification.