In Search Guard versions 3.1.1 and earlier, Field Masking (FM) rules are improperly enforced on fields of type IP (IP Address). While the content of these fields is properly redacted in the _source document returned by search operations, the results do return documents (hits) when searching based on a specific IP values. This allows to reconstruct the original contents of the field. Workaround - If you cannot upgrade immediately, you can avoid the problem by using field level security (FLS) protection on fields of the affected types instead of field masking.