CVE-2026-82761

Published Sep 17, 2026 Modified Sep 17, 2026 CWE-367

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.

Is your site exposed to CVE-2026-82761?

Run a free security scan — no signup, results in seconds.

Weakness Type (CWE)

CWE-367 CWE-367

References

Frequently Asked Questions

What is 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 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.
How do I check if I'm vulnerable to CVE-2026-82761? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-5958

When sed is invoked with both -i (in-place edit) and --follow-symlinks, the function open_next_file() performs two separate, non-atomic filesystem operations …
CVE-2026-42336

MaxKB is an open-source AI assistant for enterprise. MaxKB 2.8.0 and prior are vulnerable to a server-side request forgery (SSRF) …
CVE-2025-26620

Duende.AccessTokenManagement is a set of .NET libraries that manage OAuth and OpenId Connect access tokens. Duende.AccessTokenManagement contains a race condition …
CVE-2024-53694

A time-of-check time-of-use (TOCTOU) race condition vulnerability has been reported to affect several product versions. If exploited, the vulnerability could …
CVE-2025-32784

conda-forge-webservices is the web app deployed to run conda-forge admin commands and linting. In versions prior to 2025.4.10, a race …
CVE-2025-34027

The Versa Concerto SD-WAN orchestration platform is vulnerable to an authentication bypass in the Traefik reverse proxy configuration, allowing at …

Don't wait for an exploit

Scan your website for vulnerabilities like CVE-2026-82761 — free, no signup required.