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.

Timeline

1. Aug 31, 2026, 3:03 AM UTCCVE published
2. Aug 31, 2026, 2:49 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: partial

3. Aug 31, 2026, 2:49 PM UTCRecord last updated

Affected versions

• ash_phoenix

  From 1.2.17 · fixed in 2.3.25

• ash-project/ash_phoenix

  Version range not reported

References 4