CVE-2026-18215Network attack vector

Cross-tenant realm access via missing tenant verification

Published Jul 31, 2026 · Updated Jul 31, 2026

Improper authentication in Red Hat build of Keycloak allows remote authenticated users to enter a realm with a cross-tenant Microsoft token. The Microsoft external access-token exchange flow accepts a Microsoft Graph token without verifying its tenant ID against the configured tenant restriction. Exploitation requires a valid Microsoft Graph access token from another tenant and permits access to realm data and unauthorized realm actions.

CVSS severity6.8
Medium
EPSS probability0.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authentication in Red Hat build of Keycloak allows remote authenticated users to enter a realm with a cross-tenant Microsoft token. The Microsoft external access-token exchange flow accepts a Microsoft Graph token without verifying its tenant ID against the configured tenant restriction. Exploitation requires a valid Microsoft Graph access token from another tenant and permits access to realm data and unauthorized realm actions.

The record

CVE
CVE-2026-18215
Published
Jul 31, 2026
Updated
Jul 31, 2026
Vendor
389 Directory Server
Product
Red Hat build of Keycloak
Classifications
CWE-287, T1550.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 31, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 31, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected versions are unavailable in this record. Check the vendor advisory for version and patch details.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

389 Directory Server · Red Hat build of KeycloakAffected versions are unavailable in this record.

Published CVSS scores

8.1NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
6.8Red HatCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-287Improper Authentication
T1550.001Application Access Token

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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