CVE-2026-9803

Name: CVE-2026-9803
Creator: NVD / NIST
Published: 2026-05-28T06:16:29.75+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.3/10EPSS 0.42%

Last modified Jun 26, 2026

CVE-2026-9803 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. A flaw was found in Keycloak's ClientRegistrationAuth component. A remote unauthenticated attacker can exploit this vulnerability by sending a specially crafted POST request with a malformed 'Authorization: Bearer' header to any client registration endpoint. EPSS estimates a 0.42% chance of exploitation in the next 30 days.

Description

A flaw was found in Keycloak's ClientRegistrationAuth component. A remote unauthenticated attacker can exploit this vulnerability by sending a specially crafted POST request with a malformed 'Authorization: Bearer' header to any client registration endpoint. This can lead to an ArrayIndexOutOfBoundsException, causing the server to return an HTTP 500 error and resulting in a Denial of Service (DoS) for the affected service.

Metrics

CVSS 3.1

5.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS Probability

0.42%

33.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-125

Affected Software

Vendor	Product	Versions
Redhat	Build Of Keycloak	All versions

References

Timeline

Published: May 28, 2026
Last Modified: Jun 26, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2026-9803?

How severe is CVE-2026-9803?

CVE-2026-9803 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 0.42% probability of exploitation in the next 30 days.

How do I fix CVE-2026-9803?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-9803?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST