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CVE-2026-9803 medium CVSS 5.3

Out-of-Bounds Read in org.keycloak:keycloak-services (CVE-2026-9803)

Summary

Vulnerability in org.keycloak:keycloak-services (CVE-2026-9803). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 26.6.3 or later.

Original description

The description as published by the source.

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.

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-9803 has been found in org.keycloak:keycloak-services.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade org.keycloak:keycloak-services to 26.6.3 or later.
If unsure, ask your IT team or search "org.keycloak:keycloak-services CVE-2026-9803" on the vendor's site.

CVE-2026-9803 (org.keycloak:keycloak-services) — CWE-125 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 26.6.3 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Out-of-bounds read (CWE-125) exists in org.keycloak:keycloak-services.

📍 Affected scope

Check the vendor advisory for the affected versions of org.keycloak:keycloak-services.

🔥 Severity

Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 26.6.3.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    Audit SBOM/dependencies for affected components.

    資産台帳・SBOM・依存マニフェストで org.keycloak:keycloak-services を使っているサービスとバージョンを洗い出す。

  2. 2
    Apply patch patch 
    Upgrade org.keycloak:keycloak-services to 26.6.3

    ステージング環境で 26.6.3 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

maven org.keycloak:keycloak-services
[{"type":"ECOSYSTEM","events":[{"introduced":"26.5.0"},{"fixed":"26.6.3"}]}]

References

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