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

Published

2026-06-22

Modified

2026-07-21

EPSS percentile

34%

Aliases

GHSA-35c4-rvc8-frhm

Sources

github-advisory

Summary

## 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 UA) is neither and reaches dev workspaces too. Net effect: 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. ## Affected code [`packages/server/src/api/routes/static.ts`](https://github.com/Budibase/budibase/blob/56d2a984/packages/server/src/api/routes/static.ts) at HEAD `56d2a984` (`master`, 2026-05-18): ```ts import { permissions } from "@budibase/backend-core" import Router from "@koa/router" import { authorizedMiddleware as authorized } from "../../middleware/authorized" import recaptcha from "../../middleware/recaptcha" import { paramResource } from "../../middleware/resourceId" import * as controller from "../controllers/static" const { BUILDER, PermissionType, PermissionLevel } = permissions const router: Router = new Router() // ... router .post("/api/attachments/process", authorized(BUILDER), controller.uploadFile) .post("/api/pwa/process-zip", authorized(BUILDER), controller.processPWAZip) .post( "/api/attachments/:tableId/upload", recaptcha, paramResource("tableId"), authorized(PermissionType.TABLE, PermissionLevel.WRITE), controller.uploadFile ) // ... .post( "/api/attachments/:datasourceId/url", recaptcha, controller.getSignedUploadURL // <- no authorized(...) ) ``` Note the asymmetry: every other mutating endpoint on this router carries an `authorized(...)` middleware. The signed-URL endpoint does not. [`packages/server/src/api/controllers/static/index.ts:595-645`](https://github.com/Budibase/budibase/blob/56d2a984/packages/server/src/api/controllers/static/index.ts#L595-L645): ```ts export const getSignedUploadURL = async function (ctx) { let datasource try { const { datasourceId } = ctx.params datasource = await sdk.datasources.get(datasourceId, { enriched: true }) if (!datasource) { ctx.throw(400, "The specified datasource could not be found") } } catch (error) { ctx.throw(400, "The specified datasource could not be found") } let signedUrl, publicUrl const awsRegion = (datasource?.config?

Affected packages

Remediation: Upgrade to 3.39.0 or later.

References

• https://github.com/advisories/GHSA-35c4-rvc8-frhm