Executive Summary

CVE-2024-9666 exposes a denial‑of‑service flaw in Keycloak Server when it trusts proxy headers. Improper validation of non‑IP values in X‑Forwarded‑For or similar headers can trigger expensive DNS lookups, exhausting IO threads and rendering the service unavailable. The vulnerability requires the attacker to send crafted requests to a Keycloak instance that accepts proxy headers without overwriting them. No current CISA KEV listing.

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Authoritative CVE Metadata - CVSS Base Score: 4.7 (MEDIUM) - Published: 2024-11-25T08:15:10.943 - Last Modified: 2026-08-31T01:16:44.950

Original Description: A vulnerability was found in the Keycloak Server. The Keycloak Server is vulnerable to a denial of service (DoS) attack due to improper handling of proxy headers. When Keycloak is configured to accept incoming proxy headers, it may accept non-IP values, such as obfuscated identifiers, without proper validation. This issue can lead to costly DNS resolution operations, which an attacker could exploit to tie up IO threads and potentially cause a denial of service. The attacker must have access to send requests to a Keycloak instance that is configured to accept proxy headers, specifically when reverse proxies do not overwrite incoming headers, and Keycloak is configured to trust these headers.

"Nature takes away any faculty that is not used."

— William R. Inge