Loading a through relationship with a limit of 1 in Ash ignores the through path and returns unrelated destination records

Incorrect Authorization vulnerability in ash-project ash allows a client to read destination records unrelated to the source record through a through relationship.

When a has_many relationship declared with through: was loaded for a single record with a limit of 1, or an unsorted has_one through relationship was loaded with a limit of 1, lateral_join?/4 in lib/ash/actions/read/relationships.ex chose the path that reads the destination without any filter linking it to the source. The load returned the first destination record by sort, or any other record with an offset. The read still runs the destination's policies but carries the relationship as accessing_from, so a client paging such a field (for example teachers(limit: 1, offset: n) through AshGraphql) can enumerate destination records that policies allow only when reached through that relationship.

This issue affects ash: from 3.24.0 before 3.37.1.

Reachable when a through relationship is loaded for a single record with a caller-controlled limit of 1 (and optionally an offset), for example through AshGraphql relationship field arguments, and the destination resource's read policies rely on the relationship (accessing_from) or are otherwise open to the caller.