Is CVE-2026-9803 actively exploited?

No active exploitation of CVE-2026-9803 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2026-9803 be exploited remotely?

Yes. CVE-2026-9803 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2026-9803?

CVE-2026-9803 has a CVSS score of 5.3 (MEDIUM).

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MEDIUM

CVE-2026-9803

CWE-125Published: May 28, 2026· Updated: Jun 3, 2026

5.3

CVSS v3.1

EPSS:0.07%probability of exploitation in 30 daysPercentile:22.1th

Official 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.

NVD Source

Technical Analysis

CVE-2026-9803 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.