Server-Side Request Forgery (SSRF)

Summary

The 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. This issue affects budibase backend and server versions prior to 3.35.10.