EEF-CVE-2026-82685

## Summary

Authorization Bypass Through User-Controlled Key vulnerability in team-alembic AshAuthentication allows an authenticated attacker to overwrite and confirm another user's email address, and so take over that account. A confirmation token issued to one user is accepted on any other user's record.

`AshAuthentication.AddOn.Confirmation.ConfirmChange` verifies the token's signature and its `act` claim, then applies the changes stored against that token to whichever record the changeset targets, never comparing the `sub` claim against `changeset.data`. An attacker who registers an account and changes their own email replays the resulting token against a victim's record id, writing in their own address with `force_change_attributes/2` and stamping `confirmed_at`, after which an ordinary password reset yields the account. The library's own confirmation flow is unaffected, because `AshAuthentication.AddOn.Confirmation.Actions.confirm/3` resolves `sub` to a user and targets that record.

This issue affects ash_authentication: from 0.5.0 before 4.15.0 and from 5.0.0-rc.0 before 5.0.0-rc.14.