CVE-2018-17453: Uncovering the GitLab Vulnerability and Understanding its Exploit

CVE-2018-17453 is a security vulnerability that affected GitLab Community and Enterprise Editions in versions prior to 11.1.7, 11.2.x before 11.2.4, and 11.3.x before 11.3.1. In this post, we'll delve into the details of the issue, exploring how attackers could have exploited this vulnerability to obtain sensitive access-token data from Sentry logs via the GRPC::Unknown exception. We will also provide code snippets and links to original references to help you better understand the problem and how to avoid it in the future.

Background

GitLab is an open-source web-based Git repository management tool that provides source code management (SCM), continuous integration (CI), and continuous deployment (CD) capabilities, among other features. In late 2018, a security vulnerability was discovered that had attackers exploiting the GRPC::Unknown exception to gain access to sensitive information, specifically access-token data.

The Exploit

The vulnerability existed within GitLab's implementation of the gRPC protocol, which is used for bi-directional streaming and the client-server model. The issue stemmed from the fact that GitLab's Sentry logging system, which is designed to capture and report software crashes, exposed sensitive data by including access-token information in its logs.

Here's an example code snippet illustrating how the sensitive data was being logged

begin
  # gRPC call to external service
  external_service.call(params)
rescue GRPC::Unknown => e
  Sentry.capture_exception(e)
  raise ExternalServiceError.new(e.message)
end

When the GRPC::Unknown exception was raised, due to a software crash or any other error, the Sentry logging system captured the exception and logged the entire exception object, which inadvertently included sensitive access-token data. This access-token data would have allowed attackers to impersonate authenticated GitLab users and perform unauthorized actions.

References

To understand the issue in-depth and read about how it was discovered, you can refer to the original GitLab security advisory:

- GitLab Security Advisory: Critical security release for GitLab 11.1.7, 11.2.4, and 11.3.1

Mitigation

GitLab has since addressed this security vulnerability in its 11.1.7, 11.2.4, and 11.3.1 releases by making sure that sensitive information is not logged with the Sentry system. If you are using an affected version of GitLab, it is highly recommended that you update to the latest, secure version to avoid exposing sensitive data.

To conclude, insecure handling of sensitive information like access-token data can lead to serious security vulnerabilities. CVE-2018-17453 serves as a reminder for developers and organizations to always prioritize security in their software and to stay vigilant against potential threats, keeping systems updated to protect sensitive information from being exposed or exploited by attackers.

Timeline

Published on: 04/15/2023 23:15:00 UTC
Last modified on: 04/25/2023 20:04:00 UTC