CVE-2023-6563: An unconstrained memory consumption vulnerability was discovered in Keycloak

This month

HIGH 7.7WATCHLISTUPGRADEDOWNGRADEDOWNGRADE

CVE-2023-6563 is a high-severity flaw (CVSS 7.7) affecting keycloak, single sign-on, openshift container platform. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

High severity
Public exploit reference
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	7.7 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	1.2% (top 31%)
CISA exploited list	No
Weakness	CWE-770
Published	2023-12-14
Last modified	2026-09-22

Publisher (CNA): Red Hat, Inc. · Vendor: redhat

Last updated 2026-09-22 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2023-12-14 18:15 UTCPublished CVE record published
2026-09-22 04:17 UTCUpdated Record last modified

redhat keycloak UPGRADE

Affected: < 21.0.0

Fixed in: 21.0.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy keycloak || rpm -q keycloak || keycloak --version

2. UPGRADE to 21.0.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade keycloak

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade keycloak

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

redhat single sign-on DOWNGRADE

Affected: 7.6 · all versions

Fixed in: no fixed release known

Safe to downgrade to: a release before 7.6

1. Check installed version

apt-cache policy single-sign-on || rpm -q single-sign-on || single-sign-on --version

2. No fixed release: DOWNGRADE to a release before 7.6 (Debian / Ubuntu)

apt-cache madison single-sign-on sudo apt install single-sign-on=<VERSION_BEFORE_7.6> sudo apt-mark hold single-sign-on

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list single-sign-on sudo dnf downgrade single-sign-on-<VERSION_BEFORE_7.6> sudo dnf versionlock add single-sign-on

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

redhat openshift container platform DOWNGRADE

Affected: 4.11 · 4.12

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.11

1. Check installed version

apt-cache policy openshift-container-platform || rpm -q openshift-container-platform || openshift-container-platform --version

2. No fixed release: DOWNGRADE to a release before 4.11 (Debian / Ubuntu)

apt-cache madison openshift-container-platform sudo apt install openshift-container-platform=<VERSION_BEFORE_4.11> sudo apt-mark hold openshift-container-platform

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list openshift-container-platform sudo dnf downgrade openshift-container-platform-<VERSION_BEFORE_4.11> sudo dnf versionlock add openshift-container-platform

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

redhat openshift container platform for power DOWNGRADE

Affected: 4.9 · 4.10

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.9

1. Check installed version

apt-cache policy openshift-container-platform-for-power || rpm -q openshift-container-platform-for-power || openshift-container-platform-for-power --version

2. No fixed release: DOWNGRADE to a release before 4.9 (Debian / Ubuntu)

apt-cache madison openshift-container-platform-for-power sudo apt install openshift-container-platform-for-power=<VERSION_BEFORE_4.9> sudo apt-mark hold openshift-container-platform-for-power

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list openshift-container-platform-for-power sudo dnf downgrade openshift-container-platform-for-power-<VERSION_BEFORE_4.9> sudo dnf versionlock add openshift-container-platform-for-power

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

redhat openshift container platform for ibm linuxone DOWNGRADE

Affected: 4.9 · 4.10

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.9

1. Check installed version

apt-cache policy openshift-container-platform-for-ibm-linuxone || rpm -q openshift-container-platform-for-ibm-linuxone || openshift-container-platform-for-ibm-linuxone --version

2. No fixed release: DOWNGRADE to a release before 4.9 (Debian / Ubuntu)

apt-cache madison openshift-container-platform-for-ibm-linuxone sudo apt install openshift-container-platform-for-ibm-linuxone=<VERSION_BEFORE_4.9> sudo apt-mark hold openshift-container-platform-for-ibm-linuxone

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list openshift-container-platform-for-ibm-linuxone sudo dnf downgrade openshift-container-platform-for-ibm-linuxone-<VERSION_BEFORE_4.9> sudo dnf versionlock add openshift-container-platform-for-ibm-linuxone

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2023-6563?

keycloak: upgrade to 21.0.0; single sign-on: downgrade or apply the listed mitigation; openshift container platform: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2023-6563 being exploited?

CVE-2023-6563 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2023-6563 affect?

CVE-2023-6563 affects keycloak, single sign-on, openshift container platform. Severity is high (CVSS 7.7). 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

How urgent is CVE-2023-6563?

Priority 54/100. High severity; Public exploit reference; On your watchlist

Software pages

Keycloak vulnerabilities · Red Hat OpenShift vulnerabilities

Related CVEs

CVE-2023-6927 MEDIUM 4.6 MITIGATE DOWNGRADE A flaw was found in Keycloak
CVE-2023-6291 HIGH 7.1 UPGRADE DOWNGRADE A flaw was found in the redirect_uri validation logic in Keycloak
CVE-2023-6134 MEDIUM 4.6 UPGRADE UPGRADE A flaw was found in Keycloak that prevents certain schemes in redirects, but permits them if a wildcard is app
CVE-2025-8419 MEDIUM 5.3 MITIGATE A vulnerability was found in Keycloak-services
CVE-2025-7365 HIGH 7.1 MITIGATE A flaw was found in Keycloak

References

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