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CVE-2026-4634— Keycloak: keycloak: denial of service via excessive processing of openid connect scope parameters

Quick assessment

Affected
Red Hat Red Hat build of Keycloak 26.2
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Keycloak是Keycloak开源的一种开源身份和访问管理解决方案。 Keycloak存在安全漏洞，该漏洞源于向OIDC令牌端点发送特制的超长scope参数POST请求，可能导致资源消耗过高和处理时间延长，最终造成拒绝服务。

CVSS 7.5 · High EPSS 0.86% · P57

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 13

VendorProduct Version RangeStatus
Red Hat Red Hat build of Keycloak 26.2 26.2.15-1< * unaffected
26.2-18< * unaffected
26.2-18< * unaffected
Red Hat Red Hat build of Keycloak 26.2.15 any unaffected
Red Hat Red Hat build of Keycloak 26.4 26.4.11-1< * unaffected
26.4-14< * unaffected
26.4-14< * unaffected
Red Hat Red Hat build of Keycloak 26.4.11 any unaffected
Red Hat Red Hat Single Sign-On 7.6 for RHEL 7 0:18.0.20-1.redhat_00001.1.el7sso< * unaffected
Red Hat Red Hat Single Sign-On 7.6 for RHEL 8 0:18.0.20-1.redhat_00001.1.el8sso< * unaffected
Red Hat Red Hat Single Sign-On 7.6 for RHEL 9 0:18.0.20-1.redhat_00001.1.el9sso< * unaffected
Red Hat Red Hat Single Sign-On 7.6.13 any unaffected
Red Hat RHEL-8 based Middleware Containers 7.6-85< * unaffected
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I. Basic Information for CVE-2026-4634

Vulnerability Information
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Vulnerability Title
Keycloak: keycloak: denial of service via excessive processing of openid connect scope parameters
Source: CVE Program / CVE List V5
Vulnerability Description
A flaw was found in Keycloak. An unauthenticated attacker can exploit this vulnerability by sending a specially crafted POST request with an excessively long scope parameter to the OpenID Connect (OIDC) token endpoint. This leads to high resource consumption and prolonged processing times, ultimately resulting in a Denial of Service (DoS) for the Keycloak server.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
循环内过多的平台资源消耗
Source: CVE Program / CVE List V5
Vulnerability Title
Keycloak 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Keycloak是Keycloak开源的一种开源身份和访问管理解决方案。 Keycloak存在安全漏洞，该漏洞源于向OIDC令牌端点发送特制的超长scope参数POST请求，可能导致资源消耗过高和处理时间延长，最终造成拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Red Hat Red Hat build of Keycloak 26.2 26.2.15-1 ~ * cpe:/a:redhat:build_keycloak:26.2::el9
Red Hat Red Hat build of Keycloak 26.2 26.2-18 ~ * cpe:/a:redhat:build_keycloak:26.2::el9
Red Hat Red Hat build of Keycloak 26.2 26.2-18 ~ * cpe:/a:redhat:build_keycloak:26.2::el9
Red Hat Red Hat build of Keycloak 26.2.15 - cpe:/a:redhat:build_keycloak:26.2::el9
Red Hat Red Hat build of Keycloak 26.4 26.4.11-1 ~ * cpe:/a:redhat:build_keycloak:26.4::el9
Red Hat Red Hat build of Keycloak 26.4 26.4-14 ~ * cpe:/a:redhat:build_keycloak:26.4::el9
Red Hat Red Hat build of Keycloak 26.4 26.4-14 ~ * cpe:/a:redhat:build_keycloak:26.4::el9
Red Hat Red Hat build of Keycloak 26.4.11 - cpe:/a:redhat:build_keycloak:26.4::el9
Red Hat Red Hat Single Sign-On 7.6.13 - cpe:/a:redhat:red_hat_single_sign_on:7.6
Red Hat Red Hat Single Sign-On 7.6 for RHEL 7 0:18.0.20-1.redhat_00001.1.el7sso ~ * cpe:/a:redhat:red_hat_single_sign_on:7.6::el7
Red Hat Red Hat Single Sign-On 7.6 for RHEL 8 0:18.0.20-1.redhat_00001.1.el8sso ~ * cpe:/a:redhat:red_hat_single_sign_on:7.6::el8
Red Hat Red Hat Single Sign-On 7.6 for RHEL 9 0:18.0.20-1.redhat_00001.1.el9sso ~ * cpe:/a:redhat:red_hat_single_sign_on:7.6::el9
Red Hat RHEL-8 based Middleware Containers 7.6-85 ~ * cpe:/a:redhat:rhosemc:1.0::el8

II. Public POCs for CVE-2026-4634

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III. Intelligence Information for CVE-2026-4634

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Vendor Advisories for CVE-2026-4634 (11)

Same Patch Batch · Red Hat · 2026-04-02 · 5 CVEs total

CVE-2026-4636 8.1 HIGH Keycloak: keycloak: uma policy bypass allows authenticated users to gain unauthorized acce
CVE-2026-4282 7.4 HIGH Keycloak: keycloak: privilege escalation via forged authorization codes due to singleuseob
CVE-2026-3872 7.3 HIGH Keycloak: keycloak: information disclosure due to redirect_uri validation bypass
CVE-2026-4325 5.3 MEDIUM Keycloak: keycloak: replay of action tokens via improper handling of single-use entries

IV. Related Vulnerabilities

Same product: Red Hat build of Keycloak 26.2
Same vendor: Red Hat
Same weakness: CWE-1050

V. Comments for CVE-2026-4634

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