GHSA-j9fc-w3mr-x6mv: Budibase: Privilege escalation via public role assignment API missing app-level authorization

Budibase 3.39.19 (commit 03fbabae4) is affected by a privilege-escalation / missing-authorization flaw in the public role-assignment API. An app-scoped builder (a user who builds only specific apps — user.builder.apps = [appA], not a global builder or admin) can grant themselves builder access to ANY other app in the tenant, or assign themselves/any user an arbitrary data-plane role (e.g. ADMIN) in any app, by calling POST /api/public/v1/roles/assign. The endpoint only authorizes the two global flags (admin, builder); the per-app appBuilder and role:{appId,roleId} grant vectors are passed to the backend without any authorization check that the caller controls the target app. Reproduced in a local authorized lab using the verbatim authorization-gate and SDK logic.

This is an incomplete fix of the role-assignment hardening in commit d63d1d9054 (“Inline public user global role validation”), which only ever validated the global flags.