What’s Vulnerable › Vulnerabilities

CVE-2023-6563: Keycloak: offline session token dos

• Severity: high (CVSS 7.7 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.2% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2023-12-14 · updated 2026-09-22
• Weakness: CWE-770

Description

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 products

• Keycloak: before 21.0.0 — fixed in 21.0.0
• Red Hat OpenShift Container Platform 4.18: 4.11, 4.12
• RedHat Openshift Container Platform For Ibm Linuxone: 4.9, 4.10
• RedHat Openshift Container Platform For Power: 4.9, 4.10
• Red Hat Single Sign-On: 7.6

How to fix

Upgrade to a fixed version: Keycloak 21.0.0. Check the vendor advisory for mitigations.

References

• https://access.redhat.com/errata/RHSA-2023:7854
• https://access.redhat.com/errata/RHSA-2023:7855
• https://access.redhat.com/errata/RHSA-2023:7856
• https://access.redhat.com/errata/RHSA-2023:7857
• https://access.redhat.com/errata/RHSA-2023:7858
• https://access.redhat.com/security/cve/CVE-2023-6563
• https://bugzilla.redhat.com/show_bug.cgi?id=2253308
• https://github.com/keycloak/keycloak/issues/13340
• https://access.redhat.com/errata/RHSA-2023:7854
• https://access.redhat.com/errata/RHSA-2023:7855
• https://access.redhat.com/errata/RHSA-2023:7856
• https://access.redhat.com/errata/RHSA-2023:7857

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