CVE-2026-82761 Magic link single-use tokens replayable via TOCTOU race in AshAuthentication
Attackers can replay leaked magic link tokens to authenticate as victims due to a race condition in token revocation logic.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-82761?
CVE-2026-82761 is a critical vulnerability in team-alembic ash_authentication, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Time-of-check Time-of-use (TOCTOU) Race Condition vulnerability in team-alembic AshAuthentication allows an attacker holding a leaked magic link to replay its single-use token and authenticate as the target subject. A magic link configured with single_use_token?, which is the default, is meant to be redeemable exactly once, but nothing serialises the token's validity check against its consumption, so concurrent redemptions of one token all succeed and each yields a full user token.
Sign-in verifies the JWT with Jwt.verify/4 and revokes it only afterwards: AshAuthentication.Strategy.MagicLink.SignInPreparation revokes in a Query.after_action callback, and AshAuthentication.Strategy.MagicLink.SignInChange in an after_transaction hook that runs once the sign-in has already committed. AshAuthentication.TokenResource.Actions.revoke/3 writes the revocation as an upsert, so a concurrent duplicate revocation silently succeeds instead of conflicting and no request ever loses the race.
This issue affects ash_authentication: from 3.9.0 before 4.15.0 and from 5.0.0-rc.0 before 5.0.0-rc.14.
Weakness: CWE-367
Which versions are affected by CVE-2026-82761?
1 open source package ship an affected version, including ash_authentication.
| Package | Affected | Fixed in |
|---|---|---|
ash_authentication Hex | From 3.9.0 | 4.15.0, 5.0.0-rc.14 |
How do I fix CVE-2026-82761?
Upgrade ash_authentication to a fixed version for your release line: 4.15.0 or 5.0.0-rc.14.
Is CVE-2026-82761 being exploited?
There is no known exploitation of CVE-2026-82761 in the wild and no public exploit code.
Sources
Also known as EEF-CVE-2026-82761, GHSA-23gr-vcp4-r27q.