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

Exp

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.

Published: 2023-12-14 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2023-6563 is rated High Exploit Risk (69.3/100): CVSS High severity, with medium exploitation likelihood (EPSS 1.24%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2023-6563

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2023-6563

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.54% 1.24% +0.70%
2 2026-03-07 0.30% 0.54% +0.23%
3 2025-11-21 — 0.30% —

Full EPSS history (12 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2023-6563

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.7 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.1 4.0 [email protected]
7.7 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.1 4.0 [email protected]

Weakness enumeration for CVE-2023-6563

GitHub Security Advisory for CVE-2023-6563

GHSA-54f3-c6hg-865h · Severity: high · Ecosystem: maven — Allocation of Resources Without Limits in Keycloak

OS Trackers for CVE-2023-6563

vendor priority summary link
redhat high — https://access.redhat.com/security/cve/CVE-2023-6563

Affected software / configurations for CVE-2023-6563

Vendor Product Version Raw CPE
redhat keycloak < 21.0.0 cpe:2.3:a:redhat:keycloak:*:*:*:*:*:*:*:*
redhat single_sign-on 7.6 cpe:2.3:a:redhat:single_sign-on:7.6:*:*:*:*:*:*:*
redhat single_sign-on — cpe:2.3:a:redhat:single_sign-on:-:*:*:*:text-only:*:*:*
redhat openshift_container_platform 4.11 cpe:2.3:a:redhat:openshift_container_platform:4.11:*:*:*:*:*:*:*
redhat openshift_container_platform 4.12 cpe:2.3:a:redhat:openshift_container_platform:4.12:*:*:*:*:*:*:*
redhat openshift_container_platform_for_power 4.9 cpe:2.3:a:redhat:openshift_container_platform_for_power:4.9:*:*:*:*:*:*:*
redhat openshift_container_platform_for_power 4.10 cpe:2.3:a:redhat:openshift_container_platform_for_power:4.10:*:*:*:*:*:*:*
redhat openshift_container_platform_for_ibm_linuxone 4.9 cpe:2.3:a:redhat:openshift_container_platform_for_ibm_linuxone:4.9:*:*:*:*:*:*:*
redhat openshift_container_platform_for_ibm_linuxone 4.10 cpe:2.3:a:redhat:openshift_container_platform_for_ibm_linuxone:4.10:*:*:*:*:*:*:*

References for CVE-2023-6563

cvelogic Threat Intelligence