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.
The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Red Hat build of Keycloak 24 | RedHat | rhbk/keycloak-operator-bundle:24.0.9-1 | * |
| Red Hat build of Keycloak 24 | RedHat | rhbk/keycloak-rhel9:24-18 | * |
| Red Hat build of Keycloak 24 | RedHat | rhbk/keycloak-rhel9-operator:24-18 | * |
| Red Hat build of Keycloak 24.0.9 | RedHat | org.keycloak/keycloak-quarkus-server | * |
| Red Hat build of Keycloak 26.0 | RedHat | rhbk/keycloak-operator-bundle:26.0.6-2 | * |
| Red Hat build of Keycloak 26.0 | RedHat | rhbk/keycloak-rhel9:26.0-5 | * |
| Red Hat build of Keycloak 26.0 | RedHat | rhbk/keycloak-rhel9-operator:26.0-6 | * |
| Red Hat build of Keycloak 26.0.6 | RedHat | org.keycloak/keycloak-quarkus-server | * |
HTTP requests or responses (“messages”) can be malformed or unexpected in ways that cause web servers or clients to interpret the messages in different ways than intermediary HTTP agents such as load balancers, reverse proxies, web caching proxies, application firewalls, etc. For example, an adversary may be able to add duplicate or different header fields that a client or server might interpret as one set of messages, whereas the intermediary might interpret the same sequence of bytes as a different set of messages. For example, discrepancies can arise in how to handle duplicate headers like two Transfer-encoding (TE) or two Content-length (CL), or the malicious HTTP message will have different headers for TE and CL. The inconsistent parsing and interpretation of messages can allow the adversary to “smuggle” a message to the client/server without the intermediary being aware of it. This weakness is usually the result of the usage of outdated or incompatible HTTP protocol versions in the HTTP agents.