team-alembic ash_authentication up to 4.13.x email authentication spoofing

Summaryinfo

A vulnerability was found in team-alembic ash_authentication up to 4.13.x and classified as critical. Impacted is an unknown function. Such manipulation of the argument email leads to authentication spoofing. This vulnerability is uniquely identified as CVE-2026-49757. Local access is required to approach this attack. No exploit exists. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, has been found in team-alembic ash_authentication up to 4.13.x. Affected by this issue is an unknown code. The manipulation of the argument email with an unknown input leads to a authentication spoofing vulnerability. Using CWE to declare the problem leads to CWE-290. This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks. Impacted is confidentiality, integrity, and availability. CVE summarizes:

Authentication Bypass by Spoofing vulnerability in team-alembic AshAuthentication allows account takeover of local users via OAuth2/OIDC sign-in. AshAuthentication's OAuth2 and OIDC family strategies matched the local user by email address (an upsert on the email field, or a user-defined sign-in filter) rather than by the OpenID Connect iss/sub claim combination. Per OpenID Connect Core §5.7, only iss/sub uniquely and stably identifies an end-user; other claims, including email, MUST NOT be used as unique identifiers. A provider login presenting a victim's email, including an unverified email, a reused email, or an account with email_verified: false, resolved to and signed in as the victim's existing local account. An unauthenticated attacker who can register an account on any accepted OAuth provider with the victim's email (or who benefits from provider-side email reuse or reclamation) obtains the victim's full local privileges. The fix resolves users by the (strategy, sub) identity stored in a user identity resource, and only links a new sub to an existing local account by email when the provider's email_verified claim is trusted (trust_email_verified?). This issue affects ash_authentication from 0.1.0 before 4.14.0 and from 5.0.0-rc.0 before 5.0.0-rc.10.

The weakness was disclosed by Jarl André Hübenthal and Jonatan Männchen as GHSA-777c-2fxx-qr28. The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-49757 since 06/01/2026. The exploitation is known to be easy. The attack needs to be approached locally. No form of authentication is required for exploitation. There are known technical details, but no exploit is available.

Upgrading to version 4.14.0 or 5.0.0-rc.10 eliminates this vulnerability. Applying the patch 64530644f9b37ebb76ca14aeb83a77597a0034b7 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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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

License

• open-source

Website

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

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