AshPostgres is the PostgreSQL data layer for Ash Framework. Starting in version 2.0.0 and prior to version 2.4.10, in certain very specific situations, it was possible for the policies of an update action to be skipped. This occurred only on "empty" update actions (no changing fields), and would allow their hooks (side effects) to be performed when they should not have been. Note that this does not allow reading new data that the user should not have had access to, only triggering a side effect a user should not have been able to trigger.
To be vulnerable, an affected user must have an update action that is on a resource with no attributes containing an "update default" (updated_at timestamp, for example); can be performed atomically; does not have require_atomic? false; has at least one authorizer (typically Ash.Policy.Authorizer); and has at least one change (on the resource's changes block or in the action itself). This is where the side-effects would be performed when they should not have been.
This problem has been patched in 2.4.10 of ash_postgres. Several workarounds are available. Potentially affected users may determine that none of their actions are vulnerable using a script the maintainers provide in the GitHub Security Advisory, add require_atomic? false to any potentially affected update action, replace any usage of Ash.update with Ash.bulk_update for an affected action, and/or add an update timestamp to their action.