Skip to content

Keycloak: Application-Level DoS via Scope Processing

High severity GitHub Reviewed Published Apr 2, 2026 to the GitHub Advisory Database • Updated Apr 4, 2026

Package

maven org.keycloak:keycloak-services (Maven)

Affected versions

< 26.5.7

Patched versions

26.5.7

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.

References

Published by the National Vulnerability Database Apr 2, 2026
Published to the GitHub Advisory Database Apr 2, 2026
Reviewed Apr 4, 2026
Last updated Apr 4, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(25th percentile)

Weaknesses

Excessive Platform Resource Consumption within a Loop

The product has a loop body or loop condition that contains a control element that directly or indirectly consumes platform resources, e.g. messaging, sessions, locks, or file descriptors. Learn more on MITRE.

CVE ID

CVE-2026-4634

GHSA ID

GHSA-h4wv-g838-66g3

Source code

Loading Checking history
See something to contribute? Suggest improvements for this vulnerability.