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.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - 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. (CVE-2026-50137)

ID	Name	Product	Family	Type	Severity
443781	SCA: security update for @budibase/server (GHSA-35c4-rvc8-frhm)	Tenable Cloud Security	SCA Checks	Local	high
443781	SCA: security update for @budibase/server (GHSA-35c4-rvc8-frhm)	Tenable Self-Hosted Container Security	SCA Checks	Local	high

Detections

Analytics

CVE-2026-50137

high

Tenable Plugins

high

high