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Keycloak: Access token disclosure and implicit flow bypass via forged client data

High severity GitHub Reviewed Published May 19, 2026 to the GitHub Advisory Database • Updated Jun 4, 2026

Package

maven org.keycloak:keycloak-services (Maven)

Affected versions

< 26.6.2

Patched versions

26.6.2

Description

A flaw was found in Keycloak. A low-privilege user, with knowledge of user credentials and client ID, can bypass a security control intended to disable the implicit flow in OpenID Connect (OIDC) clients. By manipulating client data during a session restart, an attacker can obtain an access token that should not be available. This vulnerability can also lead to the exposure of these access tokens in server logs, proxy logs, and HTTP Referrer headers, resulting in sensitive information disclosure.

References

Published by the National Vulnerability Database May 19, 2026
Published to the GitHub Advisory Database May 19, 2026
Reviewed Jun 4, 2026
Last updated Jun 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
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
Low
Availability
None

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:L/UI:N/S:U/C:H/I:L/A:N

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.
(2nd percentile)

Weaknesses

External Control of Assumed-Immutable Web Parameter

The web application does not sufficiently verify inputs that are assumed to be immutable but are actually externally controllable, such as hidden form fields. Learn more on MITRE.

CVE ID

CVE-2026-7571

GHSA ID

GHSA-hq3p-w4xv-x7vp

Source code

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