Apache Polaris before version 1.4.1 has an improper input validation vulnerability (CVE-2026-42811) that allows crafted namespace or table names to bypass intended Google Cloud Storage (GCS) credential restrictions. This flaw causes the downscoped credentials, which should be limited to a single table's files, to instead grant access across the entire configured bucket. The vulnerability arises from unescaped user input in the CEL expression used to restrict access, enabling attackers to break out of the intended scope. This can lead to unauthorized listing, reading, creating, and deleting of objects beyond the authorized table path, including unrelated prefixes within the bucket. A fix is available in Apache Polaris version 1.4.1.