CVE-2026-88952: OAuth2 sign-in attached to an existing account without an email…

Description

Improper Authentication vulnerability in team-alembic AshAuthentication allows an attacker to be signed in as another user by linking an OAuth2 identity to an account that is not theirs. AshAuthentication.Strategy.OAuth2.UserResolver.resolve/3 matches an existing account using the register action's upsert_identity keys, then gates linking the incoming provider identity to it on email_trusted?/2, which reads only the provider's email_verified boolean and never compares the provider's email value with the matched account's email. That gate assumes the account was matched by its email field, so under any other upsert_identity it is vacuous and an attacker presenting their own verified email is attached to, and issued a session for, an account matched on some other attribute. The same unguarded gate applies in OAuth2.SignInPreparation on the registration_enabled? false path, where the account is matched by the sign-in action's read filter instead. The upsert also rewrites the matched account's email to the attacker's address, so later account recovery reaches the attacker rather than the owner. This issue affects ash_authentication: from 4.14.0 before 4.15.0 and from 5.0.0-rc.10 before 5.0.0-rc.14.

Scores

CVSS scores of CVE-2026-88952, by who scored it
Scored by	CVSS	Score	Vector
EEFCNA (assigner)	4.0	Critical9.1	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
NVDNVD · Deferred	4.0	Critical9.1	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/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 (exploitation in 30 days): 0.75% · top 45% of all CVEs (6 Nov 2026)
CISA SSVC: Exploitation: none · Automatable: no · Technical impact: total

The list uses the assigner's score when there is one, then CISA's, then NVD's: Critical 9.1.

Weakness

CWE-287 Improper Authentication (opens in a new tab)All about CWE-287 and its CVEs

Affected products

team-alembic · ash_authentication
- affected 4.14.0 – < 4.15.0
- affected 5.0.0-rc.10 – < 5.0.0-rc.14
team-alembic · ash_authentication
- affected 64530644f9b37ebb76ca14aeb83a77597a0034b7 – < *
- affected 42edcd8ebb13fafbb168f12591d7518ce0611fec – < *

What to do

Solution: Upgrading prevents new links but does not unpick existing ones. An account already linked through this path stays linked, and a victim's email may already have been rewritten to the attacker's address. Operators whose register action or sign-in action matched on anything other than the email should review their UserIdentity rows for links whose provider email does not match the linked account's email, and check affected accounts for a rewritten email address.

Workaround: Set trust_email_verified? false on the affected strategy, which refuses the sign-in rather than linking it and closes both the register and the sign-in path. Alternatively, key the register action's upsert_identity, or the sign-in action's read filter, on the email attribute, which restores the premise the gate assumes.

References (7)

Sources

The same CVE in the primary databases and aggregators, to check against.

Badge for a README or a ticket

[![CVE-2026-88952](https://trackcve.app/badge/CVE-2026-88952.svg)](https://trackcve.app/cve/CVE-2026-88952)

Record last updated 17 Sept 2026, 19:32 UTC.

OAuth2 sign-in attached to an existing account without an email comparison in AshAuthentication