Unauthenticated denial of service via malformed Bearer header
Published May 28, 2026 · Updated May 28, 2026
Out-of-bounds read in Red Hat build of Keycloak 26.4 and 26.6 allows remote attackers to trigger HTTP 500 errors via client registration. The ClientRegistrationAuth parser splits an Authorization Bearer header and reads a missing token element without validating the resulting array length. No authentication or special configuration is required; a malformed POST to any client registration endpoint throws an ArrayIndexOutOfBoundsException and disrupts client-registration requests.
Summary
What happened
Out-of-bounds read in Red Hat build of Keycloak 26.4 and 26.6 allows remote attackers to trigger HTTP 500 errors via client registration. The ClientRegistrationAuth parser splits an Authorization Bearer header and reads a missing token element without validating the resulting array length. No authentication or special configuration is required; a malformed POST to any client registration endpoint throws an ArrayIndexOutOfBoundsException and disrupts client-registration requests.
The record
- CVE
- CVE-2026-9803
- Published
- May 28, 2026
- Updated
- May 28, 2026
- Vendor
- 389 Directory Server
- Product
- Red Hat build of Keycloak
- Classifications
- CWE-125, T1499
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 28, 2026CVE publishedPublication date reported by the CVE source.
- May 28, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Affected versions are unavailable in this record. Check the vendor advisory for version and patch details.
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Public exploit references
- Keycloak issue 49433 reproduction stepsproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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