CVE-2026-49757: Authentication Bypass by Spoofing vulnerability in team-alembic AshAuthentication allows account takeover of local users via OAuth2/OIDC sign-in. Ash...

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.

Metrics

CVSS 4.0

9.2/10

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability

0.56%

42.5th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-290

References

Timeline

Published: Jun 15, 2026
Last Modified: Jun 17, 2026
Status: Deferred

Frequently Asked Questions

What is CVE-2026-49757?

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.

How severe is CVE-2026-49757?

CVE-2026-49757 has a CVSS score of 9.2/10 (CRITICAL severity). The EPSS model estimates a 0.56% probability of exploitation in the next 30 days.

How do I fix CVE-2026-49757?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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