Budibase: Basic app users can exfiltrate stored REST datasource auth by rewriting datasource base URL

Budibase is an open-source low-code platform. Prior to 3.39.0, the single-datasource GET and PUT routes are guarded by generic TABLE READ, not by Builder/Admin permission or datasource-specific ownership/resource checks. The built-in Basic app user role maps to the WRITE permission set, which includes table read/write and query write. A Basic user can therefore read an existing REST datasource, receive redacted authConfigs values, submit an update that changes only config.url while keeping the redacted placeholders, and trigger an existing saved relative-path REST query. During update, mergeConfigs() restores the old stored secret when it sees the redaction placeholder. During query execution, Budibase prefixes the attacker-controlled datasource config.url to the relative query path and applies the resolved stored auth headers. The result is server-side disclosure of the builder-configured REST Authorization secret to an attacker-controlled listener. This vulnerability is fixed in 3.39.0.