CVE-2024-2419: Keycloak Redirect_URI Validation Flaw Potentially Leading to Access Token Theft

A new security vulnerability, CVE-2024-2419, has been identified in Keycloak's redirect_uri validation logic. This flaw allows attackers to bypass explicitly allowed hosts and possibly steal access tokens, enabling them to impersonate other users. This vulnerability is strikingly similar to the previously reported CVE-2023-6291.

Keycloak is an open-source Identity and Access Management (IAM) solution that provides Single Sign-On (SSO) capabilities, securing applications and services with authentication and authorization. With a significant number of organizations relying on Keycloak for their security needs, this vulnerability has potentially far-reaching implications.

Exploit Details

The crux of the issue lies within Keycloak's redirect_uri validation logic. When a user attempts to log in, Keycloak checks whether the requested redirect_uri matches the list of allowed URIs configured by an administrator. However, this validation process can be tricked by simply adding specific unexpected characters in the redirect_uri, allowing an attacker to bypass the security measures.

Code Snippet - Vulnerable Keycloak Redirect_URI Validation

def is_valid_url(allowed_url, requested_url):
    """
    Check if requested_url matches allowed_url including handling of wildcards.
    """
    if '*' not in allowed_url:
        return allowed_url == requested_url

    allowed_url_parts = allowed_url.split('*')
    return all(part in requested_url for part in allowed_url_parts)

This vulnerable code snippet demonstrates a flawed implementation of the is_valid_url function, making it prone to bypass attacks.

Exploit Scenario

Imagine an application that utilizes Keycloak for user authentication with the following allowed redirect URI: https://example.com/callback.

An attacker can exploit the flaw in the validation logic by crafting a malicious URL that includes unexpected characters, such as https://example.com@evil.com/callback. As the validation logic only compares string parts (due to the wildcard splitting), it incorrectly considers this URL as valid.

With this bypass, an attacker can manipulate the login process generating an access token intended for the victim. Subsequently, the attacker steals this token and uses it to impersonate the unsuspecting user, gaining unauthorized access to secured resources.

References

- Keycloak Security Advisory CVE-2024-2419
- CVE-2024-2419 in NIST National Vulnerability Database (NVD)
- Similar Keycloak Vulnerability CVE-2023-6291
- Keycloak Official Documentation

In light of this vulnerability, it is crucial to promptly address the issue

1. Upgrade Keycloak: Ensure that you update Keycloak to the latest available version, which includes necessary security fixes. Regularly check for security updates and apply patches when necessary.

2. Restrict Redirect URIs: Apply the principle of least privilege by only allowing specific URIs necessary for intended functionalities. Avoid using wildcards whenever possible.

3. Enable Logging and Monitoring: Implement comprehensive logging and monitoring of user activities and authentication-related events. This can help detect and investigate suspicious activities, such as unauthorized access attempts or token theft.

4. Educate Your Users and Administrators: Inform your users and administrators about the risks associated with this vulnerability and provide them with guidelines to protect access tokens and recognize potential phishing attacks.

Conclusively, addressing the CVE-2024-2419 vulnerability in Keycloak's redirect_uri validation logic is of utmost priority in maintaining secure authentication and access management processes. Following the above-listed mitigation measures can significantly reduce the risk of token theft and unauthorized access to your applications and services.

Timeline

Published on: 04/17/2024 14:15:08 UTC
Last modified on: 04/17/2024 16:15:08 UTC