CVE-2026-49757 Details
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.
A vulnerability allowing authentication bypass and account takeover has been identified in Team Alembic's AshAuthentication library. This issue arises in versions 0.1.0 prior to 4.14.0 and 5.0.0-rc.0 prior to 5.0.0-rc.10. The vulnerability is rooted in the OAuth2 and OpenID Connect (OIDC) strategies, which incorrectly matched local users by email address instead of the proper OpenID Connect 'iss/sub' claim combination. According to the OpenID Connect Core specification, only the 'iss/sub' combination can uniquely and stably identify an end-user, and email should not be used as a unique identifier. As a result, an unauthenticated attacker could exploit this flaw to take over accounts of local users by registering an account with the victim's email on an OAuth provider, bypassing authentication checks, and gaining full access to the victim's account.
Users can update to AshAuthentication versions 4.14.0 or 5.0.0-rc.10, both of which include the necessary fix. After updating, it is recommended to add a UserIdentity resource using the AshAuthentication.UserIdentity extension, and to trust the email verification claim from the OAuth provider.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed Jun 15, 2026CISA-ADP
Assessed Jun 15, 2026References to Advisories, Solutions, and Tools
By selecting these links, you will be leaving this site. These are references gathered from the official CVE record and are not endorsed by Volerion.
| URL | Source(s) | Tag(s) |
|---|---|---|
| https://cna.erlef.org/cves/CVE-2026-49757.html | EEF | AdvisoryBundleVendor |
| https://github.com/team-alembic/ash_authentication/commit/64530644f9b37ebb76ca14aeb83a77597a0034b7 | EEF | Source CodeVendor |
| https://github.com/team-alembic/ash_authentication/commit/728b8d28c1b5f465fa1116ef044a815300fc733d | EEF | Source CodeVendor |
| https://github.com/team-alembic/ash_authentication/security/advisories/GHSA-777c-2fxx-qr28 | EEF | AdvisoryExploitRemedyVendor |
| https://osv.dev/vulnerability/EEF-CVE-2026-49757 | EEF | AdvisoryVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-290 | Authentication Bypass by Spoofing | EEF |
Affected Products
| Product | Versions |
|---|---|
| team-alembic AshAuthentication | >= 0.1.0, < 4.14.0 (semver) >= 5.0.0-rc.0, < 5.0.0-rc.10 (semver) |
CPE
Remediation
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Change History
3 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | EEF |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| Jun 15, 2026 | New CVE Received | EEF |