A security vulnerability has been discovered in the SAML client registration process of Keycloak (CVE-2023-6717). This flaw allows an attacker with administrative privileges or client registration access to exploit Cross-Site Scripting (XSS) by registering malicious JavaScript URIs as Assertion Consumer Service POST Binding URLs (ACS). This vulnerability can be exploited to target users in other realms or applications, executing arbitrary JavaScript in the unsuspecting users' contexts upon form submission. Consequently, the attacker can gain unauthorized access or perform malicious actions, compromising the confidentiality, integrity, and availability of the entire Keycloak instance.

Exploit Details

The vulnerability resides in Keycloak's SAML client registration process. By injecting malicious JavaScript URIs as ACS POST Binding URLs, an attacker can force the execution of arbitrary JavaScript upon form submission. This JavaScript then gains the ability to perform actions in the user's context, potentially stealing sensitive data, bypassing access controls, and causing other harmful activities.

A sample malicious ACS POST Binding URL might look like this

javascript:alert(document.cookie)

Upon form submission with this malicious URL, the JavaScript alert() function will be executed, displaying the user's cookies in an alert pop-up box.

Original References

1. Red Hat Jira Issue: KEYCLOAK-20744: SAML client registration allows registering malicious Code as ACS urls
2. Keycloak Documentation: SAML Protocol Support

Mitigation

Currently, there is no patch available for this vulnerability. However, to minimize the risk of exploitation, it is highly recommended that Keycloak administrators enforce strict access controls to client registration and monitor for suspicious activity. Additionally, consider implementing secure coding practices, such as input validation and output encoding, to prevent Cross-Site Scripting vulnerabilities.

Conclusion

CVE-2023-6717 is a critical security vulnerability in Keycloak's SAML client registration process. Exploiting this vulnerability enables an attacker to execute arbitrary JavaScript in targeted users' contexts, leading to potential security breaches and the compromise of the entire Keycloak instance. It is crucial for organizations using Keycloak to take this issue seriously and apply the recommended mitigation strategies to protect their data and infrastructure. Stay vigilant in monitoring your Keycloak instance and be prepared to act quickly once a patch is available for this vulnerability.

Timeline

Published on: 04/25/2024 16:15:10 UTC
Last modified on: 04/25/2024 17:24:59 UTC