EEF-CVE-2026-82727

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.