Budibase: POST /api/attachments/:datasourceId/url is unauthenticated and lets anonymous callers mint S3 PUT pre-signed URLs using stored datasource IAM credentials
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?.region || "eu-west-1") as string
if (datasource?.source === "S3") {
const { bucket, key } = ctx.request.body || {}
if (!bucket || !key) {
ctx.throw(400, "bucket and key values are required")
}
try {
let endpoint = datasource?.config?.endpoint
if (endpoint && !utils.urlHasProtocol(endpoint)) {
endpoint = https://${endpoint}
}
const s3 = new S3({
region: awsRegion,
endpoint,
credentials: {
accessKeyId: datasource?.config?.accessKeyId as string,
secretAccessKey: datasource?.config?.secretAccessKey as string,
},
})
const params = { Bucket: bucket, Key: key }
signedUrl = await getSignedUrl(s3, new PutObjectCommand(params))
if (endpoint) {
publicUrl = ${endpoint}/${bucket}/${key}
}
