Budibase: POST /api/attachments/:datasourceId/url is unauthenticated and lets anonymous callers mint S3 PUT pre-signed URLs using stored datasource IAM credentials
Date: 2026-06
Affected: npm/@budibase/server
Attack vector: path-traversal
Category: vulnerability-disclosure
Severity: High
CVE: CVE-2026-50137
CWE: CWE-862

## Summary The Budibase server route `POST /api/attachments/:datasourceId/url` ([`packages/server/src/api/routes/static.ts`](https://github.com/Budibase/budibase/blob/56d2a984/packages/server/src/api/routes/static.ts)) is registered with **only** the `recaptcha` middleware. There is no `authorized(...)` middleware in the chain. The controller (`packages/server/src/api/controllers/static/index.ts::getSignedUploadURL`) looks the requested datasource up, instantiates an AWS S3 client with the datasource's stored `accessKeyId` / `secretAccessKey`, and returns an AWS Signature V4 pre-signed `PutObjectCommand` URL for the caller-supplied `bucket` and `key`. The `bucket` is not pinned to the datasource's configured bucket. The workspace context required by `sdk.datasources.get` is sourced by `getWorkspaceIdFromCtx` ([`packages/backend-core/src/utils/utils.ts`](https://github.com/Budibase/budibase/blob/56d2a984/packages/backend-core/src/utils/utils.ts)) from any of: the `x-budibase-app-id` header, the JSON body `appId`, a path segment that begins with the workspace prefix, or `?appId=`. `auth.buildAuthMiddleware([], { publicAllowed: true })` runs before any of this and explicitly allows anonymous requests. The `currentWorkspace` middleware's "deny access to dev preview" branch only triggers under `isBrowser(ctx) && !isApiKey(ctx)`; `isBrowser` checks the parsed `User-Agent` for a recognised browser, so any non-browser client (curl, the supplied PoC, any tool not setting a browser U


Mitigations:

Architectural layers (MAESTRO):