How to Fix CVE-2023-25574: Critical JWT Signature Validation Vulnerability in JupyterHub LTI Authenticator?

JupyterHub is a popular platform for providing interactive computing environments to multiple users. A critical vulnerability, CVE-2023-25574, has been identified in the jupyterhub-ltiauthenticator package, specifically affecting the LTI13Authenticator class. This flaw allows an attacker to bypass authentication by forging requests, potentially granting unauthorized access to JupyterHub systems. This article provides a comprehensive overview of the vulnerability, its impact, and practical steps to remediate it, ensuring the security of your JupyterHub deployments.

A Short Introduction to JupyterHub LTI Authenticator

The jupyterhub-ltiauthenticator is a JupyterHub authenticator designed for Learning Tools Interoperability (LTI). It enables JupyterHub to authenticate users via LTI, a standard protocol for integrating educational applications. The LTI13Authenticator class, introduced in version 1.3.0, allows JupyterHub to act as an LTI tool provider, authenticating users based on LTI launches from learning management systems (LMS) like Canvas, Moodle, or Blackboard.

Summary of CVE-2023-25574

The LTI13Authenticator class, introduced in jupyterhub-ltiauthenticator version 1.3.0, fails to properly validate JWT signatures. This vulnerability allows a remote attacker to forge authentication

requests by crafting malicious JWTs that are incorrectly accepted by the JupyterHub system. The lack of proper signature validation means that the authenticator cannot verify the authenticity and integrity of the incoming authentication request. This leads to a complete breakdown of the intended authentication process. An attacker could impersonate legitimate users and gain unauthorized access. For more information, refer to what is authentication bypass.

Impact of CVE-2023-25574

The impact of CVE-2023-25574 is severe. By exploiting this vulnerability, an attacker can gain unauthorized access to JupyterHub systems without requiring any user interaction. This can lead to complete system compromise, including:

The vulnerability is network-based, meaning that an attacker can exploit it remotely, without needing physical access to the JupyterHub server. The criticality of this vulnerability necessitates immediate action to mitigate the risk. Addressing such vulnerabilities requires a robust patch management strategy.

Products Affected by CVE-2023-25574

Only users who have configured their JupyterHub installation to use the LTI13Authenticator class are affected. If you are using a different authentication method, your JupyterHub deployment is not vulnerable to this specific flaw. See the official advisory for more details.

How to Check if Your Product is Vulnerable?

To determine if your JupyterHub installation is vulnerable to CVE-2023-25574, follow these steps:

1. Check the version of jupyterhub-ltiauthenticator: Use pip show jupyterhub-ltiauthenticator or conda list jupyterhub-ltiauthenticator to determine the installed version.

2. Review your JupyterHub configuration: Examine your jupyterhub_config.py file to see if you are using the LTI13Authenticator class. Look for lines similar to the following:

If you are using jupyterhub-ltiauthenticator version 1.3.0 and the LTI13Authenticator class is configured in your JupyterHub, your installation is vulnerable.

How to Fix the Vulnerability?

The primary remediation strategy is to upgrade jupyterhub-ltiauthenticator to version 1.4.0. If immediate upgrade is not possible, disabling the LTI13Authenticator class provides a workaround.

1. Upgrade to jupyterhub-ltiauthenticator version 1.4.0:

pip install jupyterhub-ltiauthenticator==1.4.0
# or
conda install -c conda-forge jupyterhub-ltiauthenticator=1.4.0

After upgrading, restart your JupyterHub instance to apply the changes.

2. Disable the LTI13Authenticator:

If you cannot immediately upgrade, disable the LTI13Authenticator class in your jupyterhub_config.py file. Replace the following lines:

from jupyterhub_ltiauthenticator import LTI13Authenticator
c.JupyterHub.authenticator_class = LTI13Authenticator

With an alternative authenticator, such as the default PAMAuthenticator:

from jupyterhub.auth import PAMAuthenticator
c.JupyterHub.authenticator_class = PAMAuthenticator

This will disable LTI authentication and revert to the standard PAM authentication method. Ensure that you have alternative authentication mechanisms configured before disabling LTI.

Additional Security Measures:

Regardless of whether you upgrade or disable the LTI13Authenticator, consider implementing the following security measures:

By taking these steps, you can significantly reduce the risk of exploitation and protect your JupyterHub deployments from unauthorized access.

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