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Introduction

A critical vulnerability, CVE-2024-11736, was recently discovered in Keycloak, a widely-used open-source identity and access management solution. This vulnerability allows admin users to access sensitive server environment variables and system properties through user-configurable URLs.

In this blog post, we will dive deep into the details of this vulnerability, discussing its potential impact, the vulnerable code snippets within the Keycloak source code, and possible ways to exploit it. We will also provide links to the original references for further information.

Vulnerability Details

The vulnerability in Keycloak was found in the way it processes certain admin-configurable URLs, namely backchannel logout URLs and admin URLs. Admin users can include placeholders such as ${env.VARNAME} or ${PROPNAME} within these URLs. When Keycloak processes these URLs, it replaces the placeholders with their respective values, potentially exposing sensitive information to admin users.

The following code snippet from the Keycloak source code demonstrates how the vulnerability is present:

public class ConfigurableUrls {

    public UrlProcessor(String url) {
        this.url = process(url);
    }

    public String process(String url) {
        String result = url;
        result = processEnvVariables(result);
        result = processProperties(result);
        return result;
    }

    private String processEnvVariables(String url) {
        Pattern envVarPattern = Pattern.compile("\\$\\{env\\.(.+?)\\}");
        Matcher envVarMatcher = envVarPattern.matcher(url);
        StringBuffer result = new StringBuffer();
        while (envVarMatcher.find()) {
            String envVarName = envVarMatcher.group(1);
            String envVarValue = System.getenv(envVarName);
            envVarMatcher.appendReplacement(result, envVarValue);
        }
        envVarMatcher.appendTail(result);
        return result.toString();
    }

    private String processProperties(String url) {
        Pattern propPattern = Pattern.compile("\\$\\{(.+?)\\}");
        Matcher propMatcher = propPattern.matcher(url);
        StringBuffer result = new StringBuffer();
        while (propMatcher.find()) {
            String propName = propMatcher.group(1);
            String propValue = System.getProperty(propName);
            propMatcher.appendReplacement(result, propValue);
        }
        propMatcher.appendTail(result);
        return result.toString();
    }
}

As seen in the code above, the processEnvVariables and processProperties methods are responsible for replacing environment variables and system property placeholders in the URLs. By leveraging this functionality, an admin user could gain unauthorized access to potentially sensitive system information.

Possible Exploits

To exploit this vulnerability, an attacker would need admin access to a Keycloak instance. With this level of access, they could modify the backchannel logout URL or admin URL to include the desired environment variable or system property placeholders (e.g., ${env.PASSWORD} or ${SECRET_KEY}). Upon processing of these URLs by Keycloak, the attacker would be able to view the values associated with these placeholders.

Take, for example, the following URL containing a placeholder for an environment variable

https://example.com/logout?token=${env.API_KEY}

When Keycloak processes this URL, it would replace ${env.API_KEY} with the actual value of the API_KEY environment variable, potentially exposing this sensitive information to the attacker.

Original References

For more details on the CVE-2024-11736 vulnerability, including the disclosure timeline, affected versions, and possible mitigation steps, please refer to the following links:

- CVE-2024-11736: NIST National Vulnerability Database (NVD) Entry
- Official Keycloak Security Advisory

Conclusion

The CVE-2024-11736 vulnerability in Keycloak presents a potential risk for unauthorized access to sensitive system information by admin users. As such, it is crucial for organizations utilizing Keycloak to regularly update their systems to the latest version and ensure proper access controls for admin users. By staying informed about the latest security vulnerabilities and following best practices, organizations can better protect their systems and data from possible exploitation.

Timeline

Published on: 01/14/2025 09:15:20 UTC
Last modified on: 01/15/2025 05:38:20 UTC