GHSA-xh5j-727m-w6gg: Budibase vulnerable to SSRF via trivial `.tar.gz` substring bypass in Plugin URL upload (`/api/plugin`)
1. Summary| Field | Value |
|-------|-------|
| **Title** | SSRF via trivial `.tar.gz` substring bypass in Plugin URL upload |
| **Product** | Budibase (Self-Hosted) |
| **Version** | ≤ 3.34.11 (latest stable as of 2026-03-30) |
| **Component** | `packages/server/src/api/controllers/plugin/url.ts` |
| **Vulnerability Type** | CWE-918: Server-Side Request Forgery (SSRF), CWE-184: Incomplete List of Disallowed Inputs |
| **Severity** | High (chained) / Medium (standalone) |
| **CVSS 3.1 Score (chained)** | 7.7 — `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N` |
| **CVSS 3.1 Score (standalone)** | 5.4 — `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N` |
| **Attack Vector** | Network |
| **Privileges Required** | Low (Global Builder role) |
| **User Interaction** | None |
| **Affected Deployments** | All Budibase instances with plugin loading enabled (default) |2. DescriptionThe Plugin URL upload endpoint (`POST /api/plugin`) validates the submitted URL with a single substring check: `url.includes(".tar.gz")`. Any URL containing `.tar.gz` anywhere in the string — in the path, query string, or fragment — passes this check. The URL then proceeds directly to `fetchWithBlacklist()` with no further validation of host, scheme, or path.Standalone, this vulnerability is blocked by Budibase's default SSRF blacklist, which covers private IP ranges. But the URL validation layer itself is broken regardless, and it directly enables SSRF in two realistic situations: (1) when chained with the `BLACKLIST_IPS` bypass ([001]), where the blacklist is empty; and (2) when the plugin server follows HTTP redirects from an external URL to an internal target (the default `node-fetch` behavior with `redirect: 'follow'`).The developer team's own test suite (`objectStore.spec.ts:393`) tests that `downloadTarballDirect` passes through `fetchWithBlacklist` — confirming they're aware of the SSRF risk on this path. The `.tar.gz` substring check as the only URL-level guard was never intended to be the security boundary, but in practice it is.3. Root Cause Analysis3.1 Trivial substring-based URL validation**File**: `packages/server/src/api/controllers/plugin/url.ts`**Problem**: `url.includes(".tar.gz")` checks for a substring anywhere in the full URL string. It does not validate hostname, scheme, or that `.tar.gz` appears as an actual file extension at the end of the path.3.2 Bypass examples| Attack URL | `includes(".tar.gz")` | Actual request target |
|------------|----------------------|----------------------|
| `http://169.254.169.254/.tar.gz` | ✅ passes | AWS IMDS |
| `http://127.0.0.1:4005/_session.tar.gz` | ✅ passes | CouchDB |
| `http://10.0.0.1:6379/.tar.gz` | ✅ passes | Redis |
| `http://attacker.com/file.tar.gz?x=http://internal/` | ✅ passes | Redirect to internal |
| `http://internal-host/.tar.gz#fragment` | ✅ passes | Internal service |3.3 Developer awareness of SSRF risk on this path**File**: `packages/backend-core/src/objectStore/tests/objectStore.spec.ts`The team knows this code path can reach IMDS. They rely on `fetchWithBlacklist` as the defense — but never tested the `.tar.gz` substring bypass that trivially routes around it at the URL validation layer.3.4 Authorization model| Operation | Endpoint | Required Permission |
|-----------|----------|---------------------|
| Plugin URL upload | `POST /api/plugin` | Global Builder |**Key insight**: The plugin endpoint is behind `globalBuilderRoutes`, which requires Global Builder permission. This is a low-privilege role routinely granted to developers on self-hosted instances.4. Impact Analysis4.1 Confidentiality — High (chained) / Low (standalone)When chained with [001] (`BLACKLIST_IPS` bypass):**AWS/GCP/Azure IMDS** (`169.254.169.254`) — IAM credentials, service account tokens**CouchDB** (`127.0.0.1:4005`) — application databases, user records**Redis** (`127.0.0.1:6379`) — session tokens**Internal network services** (`172.16.0.0/12`, `10.0.0.0/8`)Standalone (with default blacklist active):**Open redirect chains** — if the plugin server follows redirects from external URLs to internal IPs, the blacklist check on the original URL does not protect against the redirected destination. This depends on `node-fetch` redirect behavior and whether `fetchWithBlacklist` re-checks the redirected URL.4.2 Integrity — None (GET-only path)The plugin URL upload uses GET-only semantics via `fetchWithBlacklist`. No write operations to internal services via this path.4.3 Availability — NoneNo service disruption.4.4 Scope Change (chained)Same as [001]: crosses application → infrastructure boundary when combined with the blacklist bypass.5. Proof of Concept**Verification status**: Code-level confirmed. End-to-end Docker test pending.
PoC files are ready: `poc/004_plugin_url_ssrf/poc_004_plugin_url_ssrf.py` + `docker-compose.yml`5.1 Environment Setup5.2 Step 1 — Bypass the `.tar.gz` check with a crafted URLThe `url.includes(".tar.gz")` check passes because `.tar.gz` appears in the path. The URL `http://victim:8888/.tar.gz` is not a valid tarball — but the string check doesn't know that.5.3 Step 2 — Expected response (SSRF confirmed)**With blacklist active (default config):****With `BLACKLIST_IPS=""` (chained with 001):**The `"incorrect header check"` error (zlib decompressor receiving HTTP response headers) proves the request reached `victim:8888`. The `.tar.gz` substring check was bypassed, and the HTTP fetch completed.5.4 Additional bypass payloads tested (code-level only)| URL | Check bypass | Intended target |
|-----|-------------|-----------------|
| `http://169.254.169.254/.tar.gz` | ✅ | AWS IMDS |
| `http://127.0.0.1:4005/_session.tar.gz` | ✅ | CouchDB |
| `http://127.0.0.1:6379/.tar.gz` | ✅ | Redis |
| `http://attacker.com/real.tar.gz` (redirects to `http://10.0.0.1/`) | ✅ | Internal via redirect |6. Attack ScenariosScenario A — Chained with [001]: AWS IMDS credential theftScenario B — Standalone: Open redirect SSRF (default config)Scenario C — CouchDB data access (chained)7. Affected Code Paths8. Recommended FixesFix 1 (High): Replace substring check with URL parsing and extension validationFix 2 (High): Re-check blacklist after redirect in `fetchWithBlacklist`Fix 3 (Medium): Add hostname allowlist option for plugin sourcesProvide a `PLUGIN_ALLOWED_HOSTS` variable that restricts plugin URL downloads to explicitly approved domains, rather than relying solely on a blocklist.9. References**CWE-918**: Server-Side Request Forgery (SSRF) — https://cwe.mitre.org/data/definitions/918.html**CWE-184**: Incomplete List of Disallowed Inputs — https://cwe.mitre.org/data/definitions/184.html**OWASP SSRF Prevention Cheat Sheet** — https://cheatsheetseries.owasp.org/cheatsheets/Server_Side_Request_Forgery_Prevention_Cheat_Sheet.html**Related finding**: [001] `BLACKLIST_IPS` bypass — `report/raw/001_ssrf_blacklist_bypass.md`**Developer SSRF awareness test**: `packages/backend-core/src/objectStore/tests/objectStore.spec.ts:393`
CVSS v3.1: 7.7