EEF-CVE-2026-49757 CVE-2026-49757 GHSA-777c-2fxx-qr28

OAuth2/OIDC account takeover in AshAuthentication via email-based user matching

Critical Hex

Severity: 0.0 / 10; Critical · CVSS 4.0
Exploit chance (EPSS): 0.61%; Chance of exploitation in the next 30 days. Higher than 49.48% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-290 Authentication Bypass by Spoofing
Fix: 5.0.0-rc.10; Upgrade ash_authentication to this version or later

Description

Summary

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.

Affected versions

Hex

Package	Vulnerable	Fixed in
ash_authentication	`>= 0.1.0, < 4.14.0` `>= 5.0.0-rc.0, < 5.0.0-rc.10`	`4.14.0` `5.0.0-rc.10`
ash_authentication	`>= 0.1.0, < 4.14.0`	`4.14.0`
ash_authentication	`>= 5.0.0-rc.0, < 5.0.0-rc.10`	`5.0.0-rc.10`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

ash_authentication Hex → `5.0.0-rc.10`

mix

{:ash_authentication, "~> 5.0.0-rc.10"} # then: mix deps.update ash_authentication

Severity breakdown

CVSS 4.0 0.0

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Attack vector: Network
Attack complexity: Low
Attack requirements: Present
Privileges required: None
User interaction: None
Confidentiality (vulnerable system): High
Integrity (vulnerable system): High
Availability (vulnerable system): High
Confidentiality (subsequent systems): None
Integrity (subsequent systems): None
Availability (subsequent systems): None

Weakness

CWE-290: Authentication Bypass by Spoofing

This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks.

References

Advisories

Fixes and patches

Packages

Timeline

Jun 15, 2026 Published
Oct 25, 2026 Last updated by the source
Nov 1, 2026 Latest EPSS score

Advisory	Severity	Why it's related
EEF-CVE-2026-86688 Session id is not renewed on authentication in ash_authentication, allowing session fixation	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-76949 Remember-me sign-in guard reads a session key that is never written in ash_authentication, allowing session replacement	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-91039 dynamic_oidc identities are not namespaced by connection in ash_authentication, allowing cross-connection account takeover	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-88952 OAuth2 sign-in attached to an existing account without an email comparison in AshAuthentication	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-85500 `require_confirmed_with` is not enforced on the action and fails open on an unreadable attribute in AshAuthentication	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-86533 Revoked session accepted because the session jti is never checked in AshAuthentication and AshAuthentication Phoenix	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-81632 Single-use sign-in token placed in a redirect query string in AshAuthenticationPhoenix	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-80218 Sign-in token minted for one resource accepted by another in AshAuthentication	Not rated yet	Also affects ash_authentication

Credits: James Harton, Jarl André Hübenthal, Jonatan Männchen / EEF

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