CVE-2026-50137 Budibase: POST /api/attachments/:datasourceId/url is unauthenticated and lets anonymous callers mint S3 PUT pre-signed URLs using stored datasource IAM credentials

High 8.2 Published 26 Jun 2026 Updated 29 Jun 2026

Unauthenticated attackers can mint S3 pre-signed URLs using stored IAM credentials, allowing unauthorized writes to arbitrary buckets.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2026-50137?

CVE-2026-50137 is a high-severity missing authorization vulnerability in budibase, published on 26 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Budibase is an open-source low-code platform. Prior to 3.39.0, an anonymous attacker who knows or can enumerate a workspace id (app_...) and an S3-source datasource id (ds_...) can call this endpoint with no auth and obtain a 15-minute pre-signed PUT URL minted on the victim's IAM identity. The endpoint also returns the publicUrl so the attacker knows exactly where their PUT lands. Because bucket is attacker-controlled, the attacker can write to any bucket those IAM credentials can write to, not only the bucket the datasource was configured for. The Budibase server route POST /api/attachments/:datasourceId/url (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) 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 UA) is neither and reaches dev workspaces too. This vulnerability is fixed in 3.39.0.

Weakness: CWE-862

Which versions are affected by CVE-2026-50137?

2 open source packages ship an affected version, including @budibase/server. It affects 1 product.

Package	Affected	Fixed in
`@budibase/server` npm	All versions	`3.39.0`
`@budibase/server` npm	All versions	`3.39.0`

Products include Budibase Budibase.

How do I fix CVE-2026-50137?

Upgrade @budibase/server to 3.39.0 or later.

Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.

Is CVE-2026-50137 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-50137 exists.

Sources

Also known as GHSA-35c4-rvc8-frhm.