team-alembic ash_authentication up to 4.14.x/5.0.0-rc.13 Magic Link Jwt.verify toctou

Summaryinfo

A vulnerability, which was classified as critical, has been found in team-alembic ash_authentication up to 4.14.x/5.0.0-rc.13. This impacts the function Jwt.verify of the component Magic Link. This manipulation causes toctou. This vulnerability appears as CVE-2026-82761. The attack may be initiated remotely. There is no available exploit. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in team-alembic ash_authentication up to 4.14.x/5.0.0-rc.13. It has been declared as critical. Affected by this vulnerability is the function Jwt.verify of the component Magic Link. The manipulation with an unknown input leads to a toctou vulnerability. The CWE definition for the vulnerability is CWE-367. The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. This can cause the product to perform invalid actions when the resource is in an unexpected state. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-82761 since 08/31/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details are known, but no exploit is available.

Upgrading to version 4.15.0 or 5.0.0-rc.14 eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

• team-alembic

Name

• ash_authentication

Version

• 4.0
• 4.1
• 4.2
• 4.3
• 4.4
• 4.5
• 4.6
• 4.7
• 4.8
• 4.9
• 4.10
• 4.11
• 4.12
• 4.13
• 4.14
• 5.0.0-rc.0
• 5.0.0-rc.1
• 5.0.0-rc.2
• 5.0.0-rc.3
• 5.0.0-rc.4
• 5.0.0-rc.5
• 5.0.0-rc.6
• 5.0.0-rc.7
• 5.0.0-rc.8
• 5.0.0-rc.9
• 5.0.0-rc.10
• 5.0.0-rc.11
• 5.0.0-rc.12
• 5.0.0-rc.13

Website

• Product: https://github.com/team-alembic/ash_authentication/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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