CVE-2025-12147: Unauthorized access to fields protected by Field-Level Security (FLS) when those fields are members of an object

In Search Guard FLX versions 3.1.1 and earlier, Field-Level Security (FLS) rules are improperly enforced on object-valued fields. When an FLS exclusion rule (e.g., ~field) is applied to a field which contains an object as its value, the object is correctly removed from the _source returned by search operations. However, the object members (i.e., child attributes) remain accessible to search queries. This exposure allows adversaries to infer or reconstruct the original contents of the excluded object. Workaround - If you cannot upgrade immediately and FLS exclusion rules are used for object valued attributes (like ~object), add an additional exclusion rule for the members of the object (like ~object.*).