CVE-2026-82761

published 2026-09-17

CVE-2026-82761: 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…

Priority P3 54 critical 9.1 CVSS 4.0

AV N AC L AT P PR N UI N VC H VI H VA N SC N SI N SA N E X CR X IR X AR X MAV X MAC X MAT X MPR X MUI X MVC X MVI X MVA X MSC X MSI X MSA X S X AU X R X V X RE X U X

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.

Affected

3 ranges

Vendor	Product	Version range	Fixed in
team-alembic	ash_authentication	>= 3.9.0 < 4.15.0	4.15.0
team-alembic	ash_authentication	>= 5.0.0-rc.0 < 5.0.0-rc.14	5.0.0-rc.14
team-alembic	ash_authentication	>= cf3d227ef25912cf1b0c5fa80f20001f5c46a102 < *	*

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CWE-367