EEF-CVE-2026-93477

## Summary

Improperly Controlled Modification of Dynamically-Determined Object Attributes vulnerability in ash-project ash allows a user to set the value of a private action argument on the bulk destroy and bulk update paths.

Action arguments declared with `public?: false` are meant to be set only by trusted server-side code (for example via `Ash.Changeset.set_private_argument/3`) and must not be settable from end-user input. CVE-2026-55736 fixed the non-bulk changeset path to strip private arguments from user-supplied parameter maps, but the bulk destroy and bulk update paths were not covered.

`Ash.Actions.Destroy.Bulk.base_changeset/5` and `Ash.Actions.Update.Bulk.base_changeset/5` match every key in the caller-supplied parameter map against all of the action's arguments with no `public?` check, then apply the matches to the base changeset. A caller who can submit parameters to a bulk destroy or bulk update action (for example through AshJsonApi, AshGraphql, or a controller that forwards request parameters to `Ash.bulk_destroy/4` or `Ash.bulk_update/4`) can therefore set any private argument of that action, including one referenced by an `arg(...)` template in the action's changes or validations. Depending on how the application uses the argument (for example an `acting_user_id` driving authorization or record ownership, or audit metadata), this can lead to an integrity violation or privilege escalation.

The fix requires `public?` in the argument matching on both bulk paths; private arguments remain settable server-side via the `:private_arguments` option.

This issue affects ash: from 2.17.15 before 3.33.11.

## Configurations

An action must declare a private argument (`public?: false`) that is referenced by an `arg(...)` template in one of its changes or validations, be invocable as a bulk destroy or bulk update, and the application must pass untrusted user-supplied parameters into `Ash.bulk_destroy/4` or `Ash.bulk_update/4` (directly or through AshJsonApi/AshGraphql).