Confirmation token accepted on any record in AshAuthentication

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.

Timeline

1. Sep 17, 2026, 1:08 PM UTCCVE published
2. Sep 17, 2026, 6:23 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. Sep 17, 2026, 6:23 PM UTCRecord last updated

Affected versions

• ash_authentication

  From 0.5.0 · fixed in 4.15.0; From 5.0.0-rc.0 · fixed in 5.0.0-rc.14

• team-alembic/ash_authentication

  Version range not reported

References 6