In 2023, security researchers discovered a critical flaw in the popular GitLab::API::v4 Ruby gem—a tool widely used by developers and automation scripts for interacting with GitLab servers. This vulnerability, tracked as CVE-2023-31485, is surprisingly simple yet dangerous: it does not verify TLS certificates when connecting to a GitLab server. That means anyone running scripts or tools using this gem (through version .26) could be vulnerable to man-in-the-middle (MITM) attacks.

Let’s break down what this flaw means, how it can be exploited, and what you should do to protect your code and data.

What is GitLab::API::v4?

GitLab::API::v4 is a Ruby library (or "gem") used for automating tasks and interacting with GitLab’s REST API from Ruby programs. A lot of system administrators, CI/CD engineers, and DevOps specialists rely on it to script their workflows.

The Vulnerability Explained

CVE-2023-31485 occurs because when the gem establishes an HTTPS connection to a GitLab server, it does not verify the TLS certificate. Basically, the gem says, “Hey, I trust whoever claims to be the server.” This is a huge problem because it opens the door for attackers on the network to intercept sensitive information—or even send back fake data.

Technical Details:  
In secure HTTPS connections, the client (here, your script using GitLab::API::v4) checks the server's certificate to confirm it's genuine. Skipping this check allows attackers to intercept and modify traffic without raising alarms.

Real World Risks

- Credential Theft: Attackers could steal authentication tokens, passwords, or API keys passed to the server, letting them take control of your GitLab account or repos.
- Data Manipulation: Malicious actors could inject or alter repository data, CI/CD pipelines, or deployment information.
- Supply Chain Attacks: MITM positions can allow the attacker to insert malicious code, potentially impacting entire organizations.

Let’s see a minimal example

require 'gitlab'
# Using vulnerable version: .26 or before
gitlab = Gitlab.client(
  endpoint: 'https://your.gitlab.server/api/v4';,
  private_token: 'YOUR_TOKEN'
)

# Get list of projects
projects = gitlab.projects
puts projects

With the vulnerable versions, the connection will NOT verify the server’s certificate. That means if someone on the network pretends to be your GitLab server, your script will connect to them. They’ll see everything—no alarms, no warnings.

Proof of Concept: Man-in-the-Middle

Assume an attacker can run mitmproxy or a similar tool in your network. With certificate verification off, they only need to present *any* certificate, and your script will handshake with them:

mitmproxy --mode http --listen-port 8443

Now, point your Ruby script to https://your.gitlab.server:8443/api/v4 or poison DNS/ARP to redirect traffic.

Result:
The attacker sees your authentication tokens and API traffic in cleartext. They can reply with fake data, or copy your credentials for later malicious use.

Original References

- Official CVE Record — CVE-2023-31485
- GitLab::API::v4 GitHub page
- Relevant GitHub Issue
- RubyGems Advisory

How To Fix It

Upgrade as soon as possible!

The maintainers fixed this flaw in version .27. Always use a safe and up-to-date version

gem install gitlab --version '>= .27'

Or update your Gemfile

gem 'gitlab', '>= .27'

And run

bundle update gitlab

Conclusion

CVE-2023-31485 is a classic example of how skipping basic security can lead to high-impact vulnerabilities. If you work with GitLab automation in Ruby, make sure you’re using a patched version of the gem. Otherwise, you might be giving attackers a backstage pass to your code, credentials, and more.

Stay safe, keep dependencies up to date, and always verify those certificates!


*If you want to learn more about MITM attacks or securing your API scripts, check out OWASP TLS Best Practices or the GitLab API docs.*

Timeline

Published on: 04/29/2023 00:15:00 UTC
Last modified on: 05/08/2023 17:07:00 UTC