AshPhoenix Form.Auto leaks submitted params in an unknown _union_type error message

Summary

Generation of Error Message Containing Sensitive Information vulnerability in ash-project ash_phoenix writes the entire raw submitted param map into an exception message, so secrets submitted alongside a union form field leak into logs, crash reports and the dev error page.

When AshPhoenix.Form.Auto builds a union sub-form and the submitted _union_type does not match a configured type, both raise sites built the message with inspect(params, pretty: true), embedding the full untrusted param map, and also inspected the internal union constraints[:types]. Because the message is constructed by the library rather than Phoenix's parameter logger, config :phoenix, :filter_parameters never redacts it. An attacker controls both the trigger and the contents: submitting %{"_union_type" => "nope", "password" => "..."} puts the password verbatim in the raised message. The fix reports only the offending _union_type and the valid type names, dropping the param and constraints dumps.

This issue affects ash_phoenix: from 1.2.17 before 2.3.25.

Configurations

The application renders an AshPhoenix.Form with a union field, and submitted params (which may carry secrets) reach logs, crash reports or the error page.