CVE-2023-6544 - Keycloak Security Flaw: Dynamic Client Registration and TrustedDomain Exploitable Permissive Regular Expression Vulnerability

Introduction: Security researchers have identified a critical security flaw in the widely-used Keycloak package. This vulnerability, designated as CVE-2023-6544, is due to a permissive regular expression hardcoded within the application, which specifically affects Dynamic Client Registration and TrustedDomain configuration. This article will provide an in-depth analysis of this flaw, including code snippets and links to original references, as well as exploit details that demonstrate the potential risks of this vulnerability.

Background: Keycloak is an open-source Identity and Access Management (IAM) solution that provides Single Sign-On (SSO), access control features, and authorizations to secure applications and services. It is widely adopted in various industries, making the CVE-2023-6544 security flaw a critical concern. The vulnerability reported here impacts only those instances of Keycloak with Dynamic Client Registration and TrustedDomain configuration.

Vulnerability details: The underlying issue of CVE-2023-6544 lies in a permissive regular expression hardcoded within the Keycloak package. This regular expression is used to filter out the allowed hosts that can register a dynamic client. However, due to its permissive nature, a malicious user with enough knowledge about the environment could potentially register a previously unauthorized client, leading to unauthorized access to resources protected by Keycloak.

Exploit details: To exploit this vulnerability, an attacker would first need to gather information about the environment in which the affected Keycloak instance is running. Once they've collected sufficient information, they can proceed to create a malicious client specifically aimed at registering with this vulnerable Keycloak instance, thereby gaining unauthorized access to the protected resources.

The following code snippet demonstrates the problematic regular expression within Keycloak

// Problematic regular expression allowing any valid URL that passes the check
Pattern allowedHostPattern = Pattern.compile("<INSERT_PERMISSIVE_REGEX_HERE>");

// Check if the host is allowed by comparing against the regular expression
boolean allowed = allowedHostPattern.matcher(host).matches();

Mitigations: In order to mitigate this vulnerability, users are strongly advised to update their Keycloak package to the latest version, which addresses the issue by replacing the problematic regular expression with a more restrictive one. In addition, users are suggested to limit the Dynamic Client Registration and TrustedDomain configuration using a whitelist approach.

For more information and guidance on how to address this vulnerability, please refer to the following original references:

1. Keycloak Official Documentation - Dynamic Client Registration
2. Keycloak Official Blog - Vulnerability CVE-2023-6544 - Security Advisory
3. National Vulnerability Database (NVD) - CVE-2023-6544 details and severity rating.

Conclusion: The discovery of CVE-2023-6544 highlights the importance of keeping up-to-date with security patches and updates, especially in widely-used tools like Keycloak. By understanding the nature of this vulnerability and applying proper mitigations, users can help protect their environment from potential exploitation and unauthorized access.

Timeline

Published on: 04/25/2024 15:58:47 UTC
Last modified on: 06/04/2024 17:17:10 UTC