Vulnerability · Published Jun 15, 2026 · Assigned by EEF
CVE-2026-49757OAuth2/OIDC account takeover in AshAuthentication via email-based user matching
Critical 9.2
In plain English
A critical-severity authentication bypass by spoofing in ash_authentication from team-alembic. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 50% of all known vulnerabilities).
Official description
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 products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| team-alembic | ash_authentication | 0.1.0 – before 4.14.05.0.0-rc.0 – before 5.0.0-rc.10 |
| team-alembic | ash_authentication | c5f589058e04239263f50a1430eb17ea6d5dd1a2 – before * |
Weakness: CWE-290 · Vector: 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
References
- https://github.com/team-alembic/ash_authentication/security/advisories/GHSA-777c-2fxx-qr28 vendor-advisory, related
- https://cna.erlef.org/cves/CVE-2026-49757.html related
- https://osv.dev/vulnerability/EEF-CVE-2026-49757 related
- https://github.com/team-alembic/ash_authentication/commit/728b8d28c1b5f465fa1116ef044a815300fc733d patch
- https://github.com/team-alembic/ash_authentication/commit/64530644f9b37ebb76ca14aeb83a77597a0034b7 patch