Arc is an open, SQL-native time-series database for telemetry. Prior to version 26.06.1, Arc's user-SQL validator ("internal/api/query.go:ValidateSQLRequest") blocked only "read_parquet(" and "arc_partition_agg(" via regex denylist. The broader DuckDB I/O function family — "read_csv_auto", "read_csv", "read_json", "read_json_auto", "read_text", "read_blob", "glob", "parquet_metadata", "parquet_schema", "read_xlsx", etc. — was not blocked. RBAC table-reference extraction inspected only "FROM"/"JOIN" clauses, so scalar table functions in the "SELECT" list slipped past both layers. This is fixed in 2026.06.1 via a structural sandbox at the DuckDB layer. After lockdown, DuckDB refuses to open any file outside the allowlist and refuses further "INSTALL"/"LOAD". Already-loaded extensions remain callable. Some workarounds are available. Restrict API access to known-trusted networks via firewall rules or, as a temporary mitigation, add "read_csv*"/"read_json*"/"glob" etc. to "dangerousSQLPattern" in "internal/api/query.go".