Summary
Keycloak has an Out-of-bounds Read
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.
Impact
A read operation accesses a memory location beyond the intended buffer boundary. Typical impact: sensitive data disclosure or crash.
CVE-2026-9803 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (26.6.3); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-9803? CVE-2026-9803 is a medium-severity out-of-bounds read vulnerability in org.keycloak:keycloak-services (maven), affecting versions <= 26.4.7. It is fixed in 26.6.3. A read operation accesses a memory location beyond the intended buffer boundary.
- How severe is CVE-2026-9803? CVE-2026-9803 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of org.keycloak:keycloak-services are affected by CVE-2026-9803? org.keycloak:keycloak-services (maven) versions <= 26.4.7 is affected.
- Is there a fix for CVE-2026-9803? Yes. CVE-2026-9803 is fixed in 26.6.3. Upgrade to this version or later.
- Is CVE-2026-9803 exploitable, and should I be worried? Whether CVE-2026-9803 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-9803 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-9803? Upgrade
org.keycloak:keycloak-servicesto 26.6.3 or later.