CVE-2026-9087

Modified Modified - Updated After Analysis

Keycloak Session Linking Vulnerability via IdP Identity Confusion

Publication date: 2026-05-20

Last updated on: 2026-06-26

Assigner: Red Hat, Inc.

Description

A flaw was found in Keycloak. The cross-session verification proof is keyed only by (local userId, idpAlias) and is not bound to the upstream identity that was actually verified, so a second upstream account on the same IdP can consume it and get linked to the victim's local account.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-05-20

Last Modified

2026-06-26

Generated

2026-06-30

AI Q&A

2026-05-20

EPSS Evaluated

2026-06-28

NVD

CVE-2026-9087

EUVD

EUVD-2026-31134

Affected Vendors & Products

Vendor	Product	Version / Range
redhat	build_of_keycloak	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-639	The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.

Attack-Flow Graph

Executive Summary

This vulnerability exists in Keycloak's cross-session email verification process. The verification proof is keyed only by the local user ID and the identity provider alias, but it is not bound to the specific upstream identity that was actually verified.

As a result, a second upstream account from the same identity provider can misuse this verification proof to link itself to the victim's local account.

Impact Analysis

This vulnerability can lead to unauthorized linking of accounts. An attacker controlling a second upstream account on the same identity provider can consume the verification proof intended for another user and link their account to the victim's local account.

This could result in unauthorized access or actions performed under the victim's local account, potentially compromising confidentiality and integrity of the victim's data.

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