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9.1

AshAuthentication magic link can be reused

CVE-2026-82761 · published 24 days ago
Summary

The AshAuthentication component that handles magic‑link sign‑ins may let the same one‑time link be used more than once. If an attacker obtains a link, they could log in as the intended user by submitting the link simultaneously multiple times. Upgrade to version 4.15.0 or later (or 5.0.0‑rc.14 or later) to fix the issue, and apply any available patches from the vendor.

What to do
  • Update team-alembic ash_authentication to version 9ef6864b8833d3b795427a7b8dc518a4997d41ab.
  • Update ash-project ash_authentication to version 5.0.0-rc.14.
  • Update ash_authentication to version 5.0.0-rc.14.
Affected software
Ecosystem VendorProductAffected versions
– team-alembic ash_authentication < 4.15.0
< *
Fix: upgrade to 9ef6864b8833d3b795427a7b8dc518a4997d41ab
Hex ash-project ash_authentication >= 5.0.0-rc.0, < 5.0.0-rc.14
Fix: upgrade to 5.0.0-rc.14
Hex – ash_authentication >= 5.0.0-rc.0, < 5.0.0-rc.14
Fix: upgrade to 5.0.0-rc.14
Original advisory text
Magic link single-use tokens replayable via TOCTOU race in AshAuthentication
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.
References
Fix within
Internet-facing 3 days
Internal 60 days
  • Not known to be exploited
  • Can be exploited automatically
  • Gives an attacker full control
Severity
9.1 Critical
Exploitation
<1% chance of attack within 30 days
Type
CWE-367Time-of-check Time-of-use (TOCTOU) Race Condition
Timeline
Published17 Sep 2026
Updated11 Oct 2026
First seen17 Sep 2026
Sources
CVE-2026-82761 · NVD
CVE-2026-82761 · MITRE
EEF-CVE-2026-82761 · OSV
GHSA-23gr-vcp4-r27q · GHSA
CVE-2026-82761 · OSV
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