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

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.

Published: 2026-04-02 Last update: 2026-04-16 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-4634 is rated Low Risk (32.4/100): CVSS High severity, with low exploitation likelihood (EPSS 0.02%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

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

Exploit prediction scoring system (EPSS) score for CVE-2026-4634

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 2026-05-22 0.07% 0.02% -0.04%
2 2026-04-03 — 0.07% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-4634

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
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.
 3.9 3.6 [email protected]

Weakness enumeration for CVE-2026-4634

GitHub Security Advisory for CVE-2026-4634

GHSA-h4wv-g838-66g3 · Severity: high · Ecosystem: maven — Keycloak: Application-Level DoS via Scope Processing

OS Trackers for CVE-2026-4634

vendor priority summary link
redhat high — https://access.redhat.com/security/cve/CVE-2026-4634

Affected software / configurations for CVE-2026-4634

Vendor Product Version Raw CPE
redhat build_of_keycloak — cpe:2.3:a:redhat:build_of_keycloak:-:*:*:*:text-only:*:*:*
redhat build_of_keycloak 26.2 cpe:2.3:a:redhat:build_of_keycloak:26.2:*:*:*:text-only:*:*:*
redhat build_of_keycloak 26.2.15 cpe:2.3:a:redhat:build_of_keycloak:26.2.15:*:*:*:text-only:*:*:*
redhat build_of_keycloak 26.4 cpe:2.3:a:redhat:build_of_keycloak:26.4:*:*:*:text-only:*:*:*
redhat build_of_keycloak 26.4.11 cpe:2.3:a:redhat:build_of_keycloak:26.4.11:*:*:*:text-only:*:*:*

References for CVE-2026-4634

cvelogic Threat Intelligence