GitLab Group 2FA Bypass (CVE-2025-0605): Anatomy of a Subtle Access Control Flaw

Introduction

Imagine enforcing two-factor authentication (2FA) across your GitLab groups, only to discover that users can still push code or clone repositories without ever passing a second authentication factor. This is not a hypothetical risk—CVE-2025-0605 made it a reality for thousands of organizations relying on GitLab's group access controls to enforce strong authentication. In this post, we dissect the technical root of this vulnerability, its real-world impact, and GitLab's rapid patch response.

About GitLab: GitLab is a cornerstone of the modern DevOps ecosystem, providing integrated source control, CI/CD, and project management to over 100,000 organizations globally. Its security and compliance features are widely trusted in both enterprise and open-source communities, making any authentication flaw in its platform a matter of significant concern.

Technical Information

The vulnerability at the heart of CVE-2025-0605 is a classic example of inconsistent authentication enforcement across different access vectors. When a GitLab group is configured to require 2FA, the expectation is that all users must complete a second authentication step before accessing any group resources. While this enforcement works as intended on the GitLab web interface, it broke down at the protocol level.

Vulnerability Mechanism

The flaw lies in the backend logic that handles Git protocol operations (e.g., git clone, git push). Specifically, when users authenticate via the Git CLI using their username and password, the backend failed to check whether the user had completed 2FA enrollment—even if the group policy required it. As a result, any user with valid credentials and sufficient group permissions (such as Developer or higher) could perform Git operations on repositories in 2FA-enforced groups, entirely bypassing the 2FA requirement.

This gap was not present on the web interface, where 2FA checks were correctly enforced. The inconsistency allowed attackers or insiders with valid credentials to sidestep group security policies using standard Git tooling.

Attack Vector Example

Suppose a group mandates 2FA, and a user without 2FA configured attempts to access a repository via the web UI—they are blocked and prompted to enroll in 2FA. However, the same user can run:

git clone https://gitlab.example.com/group/project.git

When prompted, they enter their username and password. Despite lacking 2FA, the operation succeeds, granting access to the repository contents. The same applies to git push and other Git operations, provided the user has the necessary permissions.

Root Cause

The root cause is a missing or improperly implemented 2FA check in the authentication logic for Git protocol endpoints. The backend did not consistently enforce group-level 2FA requirements outside the web interface, creating a gap that could be exploited by anyone with valid credentials and group access.

CWE Classification:

CWE-1390: Weak Authentication
CWE-287: Improper Authentication

Patch Information

In the GitLab 18.0.1 patch release, several critical vulnerabilities were addressed to enhance the platform's security and stability. One significant fix involved securing the large blob endpoint, which previously allowed authenticated attackers to exhaust server resources, leading to denial-of-service conditions. The patch introduced proper access controls and resource management to prevent such exploitation.

Another important update corrected improper XPath validation in SAML responses. This flaw permitted modified SAML responses to bypass two-factor authentication requirements under specific conditions. The fix involved strengthening the validation mechanisms to ensure that only properly authenticated responses are processed.

Additionally, the release addressed an issue with Discord webhook integrations that could cause denial-of-service attacks. By implementing stricter input validation and rate limiting, the patch mitigated the risk of service disruption through this vector.

For users utilizing Kubernetes integrations, the patch resolved a vulnerability where unbounded cluster tokens could lead to denial-of-service scenarios. The update enforced limits on token generation and included proper validation checks to prevent abuse.

Furthermore, the patch fixed an issue where unvalidated note positions could be exploited to cause denial-of-service conditions. By implementing thorough validation of note positions, the update ensured that only legitimate inputs are processed, thereby maintaining system integrity.

These updates collectively reinforce GitLab's commitment to providing a secure and reliable platform for its users.

Patch source: GitLab 18.0.1 Patch Release

Affected Systems and Versions

CVE-2025-0605 affects the following GitLab versions:

GitLab CE/EE 16.8 up to (but not including) 17.10.7
GitLab CE/EE 17.11.0 up to (but not including) 17.11.3
GitLab CE/EE 18.0.0 (fixed in 18.0.1)

Any group configured to require 2FA is vulnerable if running one of these versions. The vulnerability is present regardless of deployment method (self-hosted, cloud, etc.) as long as the affected version is in use and group-level 2FA is enabled.

Vendor Security History

GitLab has a strong track record of transparent security practices, including a public bug bounty program and regular security releases. The response to CVE-2025-0605 was notably fast, with patches released within a day of disclosure. However, authentication and access control issues have recurred in GitLab's history (e.g., CVE-2024-12093), indicating the complexity and ongoing challenge of securing such a feature-rich platform.

References

Source: This report was created using AI

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