CVE-2024-9666
MediumCVSS 4.7Exploitation Probability (EPSS)
Low risk34th percentile - higher than 34% of all known CVEs
Summary
A vulnerability was found in Keycloak Server, making it vulnerable to denial of service due to improper handling of proxy headers. When configured to accept incoming proxy headers, it may accept non-IP values without validation, leading to costly DNS resolution operations that can tie up IO threads and cause DoS. The attacker must have access to a Keycloak instance configured to accept proxy headers, especially when reverse proxies do not overwrite incoming headers.
Risk Assessment
An attacker can overload the Keycloak server, causing unavailability of authentication and authorization services. This can affect all systems relying on Keycloak.
Recommendation
Configure reverse proxies to overwrite proxy headers and do not trust incoming headers. Update Keycloak to a patched version.
Other vulnerabilities in Keycloak
See all- CVE-2026-101333Low
A flaw in the Micrometer user-event metrics listener of Keycloak occurs when the listener is configured to include the idp tag. An unauthenticated attacker can send requests to the identity broker login endpoint using arbitrary provider aliases, causing the system to create an unlimited number of metric time series, leading to excessive memory consumption and degraded performance of the server and monitoring tools.
- CVE-2026-19607Medium
A flaw was found in the first-broker-login flow of the keycloak-services component. It allows an attacker to register a matching username on an external identity provider, causing a collision in Keycloak and locking out the legitimate user.
- CVE-2026-17526High
Keycloak is an open-source identity and access management solution. A vulnerability was discovered where a user with the impersonation role can impersonate a realm administrator, gaining full administrative control over the realm, including the ability to manage users, clients, and roles.
- CVE-2026-79651High
A flaw was found in the theme localization endpoints of the keycloak-services component, which is the core service responsible for authentication flows and theme management in Keycloak. The issue occurs because the system accepts arbitrary locale tags from unauthenticated requests and stores them in a permanent in-memory cache without limits. An attacker can exploit this by sending a large number of unique locale tags, eventually causing the server to run out of memory and crash.
- CVE-2026-18212High
A flaw was found in the SAML Redirect Binding implementation of Keycloak where the custom DEFLATE compression and decompression helpers fail to release native zlib memory after use. An unauthenticated attacker can exploit this by sending repeated malformed SAML requests, leading to native memory exhaustion and a denial of service.
- CVE-2026-19608Medium
A flaw was found in the group policy provider of Keycloak authorization services, which is used to manage fine-grained access control to resources. The issue occurs when the system evaluates group-based policies using tokens that only contain group names rather than full paths. If two groups in different parts of the organization share the same name, a user in the unauthorized group can be mistaken for a member of the authorized group. This can allow a user to gain unauthorized access to protected resources they should not be able to reach.
- CVE-2017-12159High
It was found that the cookie used for CSRF prevention in Keycloak was not unique to each session. An attacker could use this flaw to gain access to an authenticated user session, leading to possible information disclosure or further attacks.
- CVE-2026-118959Medium
A flaw was found in the required action provider mechanism of Keycloak. When an authorization request includes the kc_action query parameter set to a mandatory action already assigned to the user (such as profile verification or terms and conditions), Keycloak may skip these mandatory challenges and issue an authorization code.
- CVE-2026-118947Medium
A flaw was found in the UMA resource registration endpoint of the keycloak-services component. When remote resource management is enabled, an authenticated user with specific permissions can update resources they do not own by providing a target resource ID in a request.
- CVE-2026-118425Medium
A flaw was found in the secure-redirect-uris-enforcer client policy of Keycloak, an identity and access management solution. The issue occurs when the policy is configured to allow loopback addresses, as Keycloak resolves hostnames via DNS during validation. An attacker can bypass domain allowlist restrictions by using a hostname that resolves to a loopback address, potentially allowing the registration of unauthorized redirect URIs.
Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

