Executive brief
Budibase is a low-code platform that allows organizations to build and deploy business applications. A critical flaw in its file-attachment endpoint allows unauthenticated attackers to generate temporary URLs that grant S3 write access using the application's stored AWS credentials. An attacker can upload files to any AWS S3 bucket the application has access to, potentially compromising sensitive data, injecting malware, or disrupting operations.
Technical details
The vulnerability is an authentication bypass in the POST /api/attachments/:datasourceId/url endpoint (packages/server/src/api/routes/static.ts). Unlike all other mutating endpoints on the same router, this endpoint lacks the authorized(...) middleware, instead relying only on recaptcha middleware which is disabled by default and skipped for non-production workspaces. The controller (getSignedUploadURL) accepts an attacker-supplied bucket and key parameter, then uses sdk.datasources.get() to retrieve S3 credentials for the specified datasource and instantiates an AWS S3 client with those credentials. It returns an AWS Signature V4 pre-signed PutObjectCommand URL valid for 15 minutes. The workspace context is derived from the x-budibase-app-id header, body appId, path segment, or query parameter, and auth.buildAuthMiddleware runs with publicAllowed: true. The currentWorkspace dev-preview check bypasses non-browser clients (such as curl or custom tools), allowing access to development workspaces. An attacker must know or enumerate a workspace ID (app_...) and datasource ID (ds_...), both trivially enumerable in many deployments. The fix is available in version 3.39.0 and later.
Affected products
- Budibase @budibase/server <3.39.0
Timeline
- 2026-05-28: disclosed
- 2026-05-28: patched: Patched in version 3.39.0