---
id: CVE-2023-6563
title: An unconstrained memory consumption vulnerability was discovered in Keycloak
summary: >-
  An unconstrained memory consumption vulnerability was discovered in Keycloak.
  It can be triggered in environments which have millions of offline tokens (>
  500,000 users with each having at least 2 saved sessions). If an attacker
  creates …
severity: high
cvss: 7.7
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H'
cwe:
  - CWE-770
vendor: redhat
product: keycloak
affected:
  - keycloak < 21.0.0
  - single_sign-on = 7.6
  - single_sign-on
  - openshift_container_platform = 4.11
  - openshift_container_platform = 4.12
  - openshift_container_platform_for_power = 4.9
  - openshift_container_platform_for_power = 4.10
  - openshift_container_platform_for_ibm_linuxone = 4.9
  - openshift_container_platform_for_ibm_linuxone = 4.10
patched:
  - keycloak 21.0.0
published: '2023-12-14'
updated: '2026-09-22'
sourceUpdated: '2026-09-22T04:17:56.693'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2023-6563'
references:
  - url: 'https://access.redhat.com/errata/RHSA-2023:7854'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2023:7855'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2023:7856'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2023:7857'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2023:7858'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/security/cve/CVE-2023-6563'
    label: secalert@redhat.com
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2253308'
    label: secalert@redhat.com
  - url: 'https://github.com/keycloak/keycloak/issues/13340'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2023:7854'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://access.redhat.com/errata/RHSA-2023:7855'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://access.redhat.com/errata/RHSA-2023:7856'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://access.redhat.com/errata/RHSA-2023:7857'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://access.redhat.com/errata/RHSA-2023:7858'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://access.redhat.com/security/cve/CVE-2023-6563'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2253308'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://github.com/keycloak/keycloak/issues/13340'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2023/cve-2023-6563.json
  - url: 'https://www.cve.org/CVERecord?id=CVE-2023-6563'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2023-6563'
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
epss: 0.01239
epssPercentile: 0.67817
ingestedAt: '2026-09-22T03:57:48.898Z'
---

## Overview

An unconstrained memory consumption vulnerability was discovered in Keycloak. It can be triggered in environments which have millions of offline tokens (> 500,000 users with each having at least 2 saved sessions). If an attacker creates two or more user sessions and then open the "consents" tab of the admin User Interface, the UI attempts to load a huge number of offline client sessions leading to excessive memory and CPU consumption which could potentially crash the entire system.

## Affected

- `keycloak < 21.0.0`
- `single_sign-on = 7.6`
- `single_sign-on`
- `openshift_container_platform = 4.11`
- `openshift_container_platform = 4.12`
- `openshift_container_platform_for_power = 4.9`
- `openshift_container_platform_for_power = 4.10`
- `openshift_container_platform_for_ibm_linuxone = 4.9`
- `openshift_container_platform_for_ibm_linuxone = 4.10`

## Remediation

Upgrade past the affected range:

- `keycloak 21.0.0`

## Vendor advisories

- **RHSA-2023:7854** · Red Hat · fixed in: Red Hat Single Sign-On 7.6 for RHEL 7 Server · released 2023-12-14 · [advisory](https://access.redhat.com/errata/RHSA-2023:7854)
- **RHSA-2023:7857** · Red Hat · fixed in: Middleware Containers for OpenShift · released 2023-12-14 · [advisory](https://access.redhat.com/errata/RHSA-2023:7857)
- **RHSA-2023:7856** · Red Hat · fixed in: Red Hat Single Sign-On 7.6 for RHEL 8 · released 2023-12-14 · [advisory](https://access.redhat.com/errata/RHSA-2023:7856)
- **RHSA-2023:7855** · Red Hat · fixed in: Red Hat Single Sign-On 7.6 for RHEL 9 · released 2023-12-14 · [advisory](https://access.redhat.com/errata/RHSA-2023:7855)
- **RHSA-2023:7858** · Red Hat · fixed in: Single Sign-On 7.6.6 · released 2023-12-14 · [advisory](https://access.redhat.com/errata/RHSA-2023:7858)