This chapter discusses possible security vulnerabilities Keycloak could have, how Keycloak mitigates those vulnerabilities, and what steps you need to do to configure Keycloak to mitigate some vulnerabilities. A good list of potential vulnerabilities and what security implementations should do to mitigate them can be found in the OAuth 2.0 Thread Model document put out by the IETF. Many of those vulnerabilities are discussed here.

If you do not use SSL/HTTPS for all communication between the Keycloak auth server and the clients it secures you will be very vulnerable to man in the middle attacks. OAuth 2.0/OpenID Connect uses access tokens for security. Without SSL/HTTPS, attackers can sniff your network and obtain an access token. Once they have an access token they can do any operation that the token has been given permission for. Keycloak has three modes for SSL/HTTPS. SSL can be hard to set up, so out of the box, Keycloak allows non-HTTPS communication over private IP addresses like localhost, 192.168.x.x, and other private IP addresses. In production, you should make sure SSL is enabled and required across the board. On the adapter/client side, Keycloak allows you to turn off the SSL trust manager. The trust manager ensures identity the client is talking to. It checks the DNS domain name against the server's certificate. In production you should make sure that each of your client adapters is configured to use a truststore. Otherwise you are vulnerable to DNS man in the middle attacks.

Cross-site request forgery (CSRF) is a web-based attack whereby HTTP requests are transmitted from a user that the web site trusts or has authenticated (e.g., via HTTP redirects or HTML forms). Any site that uses cookie based authentication is vulnerable for these types of attacks. These attacks are mitigated by matching a state cookie against a posted form or query parameter. OAuth 2.0 login specification requires that a state cookie be used and matched against a transmitted state parameter. Keycloak fully implements this part of the specification so all logins are protected. The Keycloak adminstration console is a pure Javascript/HTML5 application that makes REST calls to the backend Keycloak admin API. These calls all require bearer token authentication and are made via Javascript Ajax calls. CSRF does not apply here. The admin REST API can also be configured to validate CORS origins as well. The only part of Keycloak that really falls into CSRF is the user account management pages. To mitigate this Keycloak sets a state cookie and also embeds the value of this state cookie within hidden form fields or query parameters in action links. This query or form parameter is checked against the state cookie to verify that the call was made by the user.

With clickjacking, a malicious site loads the target site in a transparent iFrame overlaid on top of a set of dummy buttons that are carefully constructed to be placed directly under important buttons on the target site. When a user clicks a visible button, they are actually clicking a button (such as an "Authorize" button) on the hidden page. An attacker can steal a user's authentication credentials and access their resources. By default, every response by Keycloak sets some specific browser headers that can prevent this from happening