CVE-2026-50136

Description

The application server exposes an unauthenticated endpoint that generates S3 `PutObject` presigned URLs using credentials stored in a workspace datasource. The route is protected only by the recaptcha middleware and does not require authentication, table permission, datasource permission, or builder access. A public caller who knows a workspace ID and S3 datasource ID can request a signed upload URL for attacker-controlled bucket and key values. ### Details The static route registers the signed upload URL endpoint with only `recaptcha` before the controller: - `packages/server/src/api/routes/static.ts:44-48` ```ts 44: .post( 45: "/api/attachments/:datasourceId/url", 46: recaptcha, 47: controller.getSignedUploadURL 48: ) ``` The controller loads the datasource by `datasourceId` with enriched secret values: - `packages/server/src/api/controllers/static/index.ts:590-598` ```ts 590:export const getSignedUploadURL = async function ( 591: ctx: Ctx<GetSignedUploadUrlRequest, GetSignedUploadUrlResponse> 592:) { 593: // Ensure datasource is valid 594: let datasource 595: try { 596: const { datasourceId } = ctx.params 597: datasource = await sdk.datasources.get(datasourceId, { enriched: true }) 598: if (!datasource) { ``` The request body controls `bucket` and `key`, and the server signs a PUT URL using the stored datasource credentials: - `packages/server/src/api/controllers/static/index.ts:609-629` ```ts 609: if (datasource?.source === "S3") { 610: const { bucket, key } = ctx.request.body || {} 611: if (!bucket || !key) { 612: ctx.throw(400, "bucket and key values are required") 613: } 614: try { 615: let endpoint = datasource?.config?.endpoint 616: if (endpoint && !utils.urlHasProtocol(endpoint)) { 617: endpoint = `https://${endpoint}` 618: } 619: const s3 = new S3({ 620: region: awsRegion, 621: endpoint: endpoint, 622: credentials: { 623: accessKeyId: datasource?.config?.accessKeyId as string, 624: secretAccessKey: datasource?.config?.secretAccessKey as string, 625: }, 626: }) 627: const params = { Bucket: bucket, Key: key } 628: signedUrl = await getSignedUrl(s3, new PutObjectCommand(params)) 629: if (endpoint) { ``` The endpoint returns the signed URL and public URL to the caller: - `packages/server/src/api/controllers/static/index.ts:630-639` ```ts 630: publicUrl = `${endpoint}/${bucket}/${key}` 631: } else { 632: publicUrl = `https://${bucket}.s3.${awsRegion}.amazonaws.com/${key}` 633: } 634: } catch (error: any) { 635: ctx.throw(400, error) 636: } 637: } 638: 639: ctx.body = { signedUrl, publicUrl } ``` Because no authorization middleware is applied, the API trusts public input to choose where the stored S3 credentials will write. ### PoC Non-destructive validation approach: 1. Create or identify a workspace with an S3 datasource. 2. Obtain the production workspace ID and S3 datasource ID. 3. Send an unauthenticated request with the workspace ID header and attacker-controlled bucket/key: ```http POST /api/attachments/<datasourceId>/url HTTP/1.1 x-budibase-app-id: app_<workspace-id> content-type: application/json {"bucket":"attacker-controlled-or-permitted-bucket","key":"poc/budibase.txt"} ``` 4. Observe that the response contains a signed PUT URL. 5. Upload harmless content to the returned `signedUrl` and confirm the object is created using the datasource's stored S3 credentials. ### Impact This allows unauthenticated arbitrary object writes wherever the stored S3 datasource credentials have `PutObject` access. Depending on the datasource permissions, this can corrupt application data, overwrite public assets, place attacker-controlled objects in trusted buckets, consume storage, or abuse an organization's cloud credentials.