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

Summary

CVE	CVE-2026-49757
State	PUBLISHED
Assigner	EEF
Source Priority	CVE Program / NVD first with legacy fallback
Published	2026-06-15 12:16:25 UTC
Updated	2026-06-15 20:55:48 UTC
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.

Risk And Classification

Primary CVSS: v4.0 9.2 CRITICAL from 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

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

Problem Types: CWE-290 | CWE-290 CWE-290 Authentication Bypass by Spoofing

Version	Source	Type	Score	Severity	Vector
4.0	6b3ad84c-e1a6-4bf7-a703-f496b71e49db	Secondary	9.2	CRITICAL	`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/C...`
4.0	CNA	CVSS	9.2	CRITICAL	`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`

CVSS v4.0 Breakdown

Attack Vector

Network

Attack Complexity

Low

Attack Requirements

Present

Privileges Required

None

User Interaction

None

Confidentiality

High

Integrity

High

Availability

High

Sub Conf.

None

Sub Integrity

None

Sub Availability

None

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

Vendor Declared Affected Products

Source	Vendor	Product	Version	Platforms
CNA	Team-alembic	Ash Authentication	affected 0.1.0 4.14.0 semver	Not specified
CNA	Team-alembic	Ash Authentication	affected 5.0.0-rc.0 5.0.0-rc.10 semver	Not specified
CNA	Team-alembic	Ash Authentication	affected c5f589058e04239263f50a1430eb17ea6d5dd1a2 * git	Not specified

References

Reference	Source	Link	Tags
github.com/team-alembic/ash_authentication/commit/728b8d28c1b5f465fa1116...	6b3ad84c-e1a6-4bf7-a703-f496b71e49db	github.com
osv.dev/vulnerability/EEF-CVE-2026-49757	6b3ad84c-e1a6-4bf7-a703-f496b71e49db	osv.dev
github.com/team-alembic/ash_authentication/commit/64530644f9b37ebb76ca14...	6b3ad84c-e1a6-4bf7-a703-f496b71e49db	github.com
cna.erlef.org/cves/CVE-2026-49757.html	6b3ad84c-e1a6-4bf7-a703-f496b71e49db	cna.erlef.org
github.com/team-alembic/ash_authentication/security/advisories/GHSA-777c...	6b3ad84c-e1a6-4bf7-a703-f496b71e49db	github.com
CVE Program record	CVE.ORG	www.cve.org	canonical
NVD vulnerability detail	NVD	nvd.nist.gov	canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Jarl André Hübenthal (en)

CNA: James Harton (en)

CNA: Jonatan Männchen / EEF (en)

There are currently no legacy QID mappings associated with this CVE.