CVE-2026-9803Keycloak: keycloak: denial of service via malformed authorization header
- 5.3MediumCVSS base score
- 0.42%Exploitation in 30 daysEPSS · top 63% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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.
Timeline
ID reserved
By redhat
Published
- 29 days later
· 29 days later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| redhatCNA (assigner) | 3.1 | Medium5.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L |
| NVDNVD · Modified | 3.1 | Medium5.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L |
- EPSS (exploitation in 30 days)
- 0.42% · top 63% of all CVEs (14 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: yes · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.3.
Affected products
Red Hat · Red Hat build of Keycloak 26.4
- unaffected 26.4.13-1 – < *
Red Hat · Red Hat build of Keycloak 26.4
- unaffected 26.4-19 – < *
Red Hat · Red Hat build of Keycloak 26.4
- unaffected 26.4-19 – < *
Red Hat · Red Hat build of Keycloak 26.4.13
All versions: unaffected
Red Hat · Red Hat build of Keycloak 26.6
- unaffected 26.6.3-3 – < *
Red Hat · Red Hat build of Keycloak 26.6
- unaffected 26.6-6 – < *
Red Hat · Red Hat build of Keycloak 26.6
- unaffected 26.6-6 – < *
Red Hat · Red Hat build of Keycloak 26.6.3
All versions: unaffected
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- Mavenorg.keycloak:keycloak-servicesGHSA-cpf7-j4cf-vqx4 (opens in a new tab)
What to do
Workaround: Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
References
References6
- RHSA-2026:25097 (opens in a new tab)vendor-advisoryx_refsource_REDHAT
- RHSA-2026:25098 (opens in a new tab)vendor-advisoryx_refsource_REDHAT
- RHSA-2026:30049 (opens in a new tab)vendor-advisoryx_refsource_REDHAT
- RHSA-2026:30050 (opens in a new tab)vendor-advisoryx_refsource_REDHAT
- https://access.redhat.com/security/cve/CVE-2026-9803 (opens in a new tab)vdb-entryx_refsource_REDHAT
- RHBZ#2482465 (opens in a new tab)issue-trackingx_refsource_REDHAT
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-32719 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-cpf7-j4cf-vqx4 (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-9803)Record last updated .