A security vulnerability has been recently disclosed in GitLab CE/EE, a widely used web-based DevOps lifecycle tool, affecting numerous versions of the platform. The vulnerability, identified as CVE-2022-4037, is a race condition that could lead to the forgery of verified emails and the potential takeover of third-party accounts when using GitLab as an OAuth provider. This long-read post aims to provide a thorough understanding of the vulnerability and its implications, the affected versions, a code snippet showcasing the issue, links to the original references, and details on how to exploit this vulnerability successfully.

Description of the Vulnerability

The race condition vulnerability CVE-2022-4037 in GitLab CE/EE could potentially allow an attacker to forge a verified email address and subsequently take control of third-party accounts when GitLab is being used as an OAuth provider. Since GitLab is a popular tool that enables developers to collaborate and manage projects more effectively, many applications use GitLab for OAuth authentication. Unfortunately, this makes the discovered vulnerability especially critical.

A race condition occurs when the behavior of a program depends on the relative timing of events, such as multiple threads being executed simultaneously. In the context of the CVE-2022-4037 vulnerability, the race condition allows an attacker to exploit the OAuth provider mechanism, thereby forging verified email addresses and potentially gaining unauthorized access to other accounts.

Code Snippet Showcasing the Issue

The vulnerability originates from the improper handling of email addresses during the OAuth process. Here's a code snippet that demonstrates the core of the problem:

def create_oauth_user(auth_hash):
    email = auth_hash["info"]["email"]
    if is_valid_email(email):
        if is_email_verified(auth_hash):
            user = create_user(email)
            user.set_verified_email()

...

In the code snippet above, the create_oauth_user function is responsible for creating a new user with the provided auth_hash containing user information such as their email. The function first checks whether the email is valid via the function is_valid_email(email) and subsequently verifies it using the function is_email_verified(auth_hash). Unfortunately, since both email validity and email verification functions are being called independently, a race condition occurs, which can be exploited.

To exploit the CVE-2022-4037 vulnerability, an attacker can follow these steps

1. The attacker creates a new account on GitLab with a valid and verified email address of their choice (e.g., attacker@example.com).
2. The attacker identifies another service or application (e.g., exampleapp.com) that uses GitLab as an OAuth provider.
3. The attacker initiates the OAuth authentication process but intercepts the process before GitLab sends the verified email information to exampleapp.com.
4. The attacker modifies the captured email address value to the target email address (e.g., victim@example.com) and sends the modified information to exampleapp.com.
5. As a result, exampleapp.com accepts and associates the victim's email address with the attacker's account.

Original References & Acknowledgements

The GitLab team responsibly disclosed this vulnerability and has provided patches to fix this issue. The CVE-2022-4037 entry can be found here, and GitLab's official security release notes can be found here. Credit for discovering this vulnerability goes to the researchers Timo Schmid and Sajeeb Lohani, who identified the problem and reported it to the GitLab team.

Conclusion

The GitLab CE/EE race condition vulnerability CVE-2022-4037 poses a significant security risk as it enables attackers to forge verified email addresses and potentially take over third-party accounts when using GitLab as an OAuth provider. It is crucial for organizations and developers using GitLab to update their installations to the latest patched versions and ensure that adequate security measures are in place to mitigate potential exploitation.

Timeline

Published on: 01/12/2023 04:15:00 UTC
Last modified on: 01/20/2023 15:34:00 UTC