CVE-2021-21411 Explained : Impact and Mitigation

OAuth2-Proxy, an open-source reverse proxy, encountered a critical vulnerability related to group-based authorization in the GitLab provider. Here's what you need to know about CVE-2021-21411.

Understanding CVE-2021-21411

OAuth2-Proxy suffered from an issue where the authorization mechanism failed to restrict access based on group membership, impacting GitLab Provider users relying on this feature.

What is CVE-2021-21411?

In OAuth2-Proxy version 7.0.0, the

--gitlab-group

flag for group-based authorization in the GitLab provider was ineffective, allowing any authenticated users to access applications without proper restrictions.

The Impact of CVE-2021-21411

The vulnerability allowed unauthorized access in GitLab environments using OAuth2-Proxy, potentially exposing critical applications to unauthorized users.

Technical Details of CVE-2021-21411

The vulnerability stemmed from a bug in the authorization logic, allowing users to bypass group-based restrictions.

Vulnerability Description

OAuth2-Proxy incorrectly populated the user session's groups field with

--gitlab-group

config entries instead of fetching individual user group memberships, leading to improper authorization checks.

Affected Systems and Versions

OAuth2-Proxy versions >= 7.0.0 and < 7.1.0 are affected by this vulnerability.

Exploitation Mechanism

Unauthorized users could gain access to applications due to the incorrect implementation of group-based authorization checks.

Mitigation and Prevention

It is crucial to take immediate steps to address the vulnerability and prevent unauthorized access to sensitive resources.

Immediate Steps to Take

Update OAuth2-Proxy to version 7.1.0 or higher to patch the vulnerability and ensure secure access controls.

Long-Term Security Practices

Regularly review and update authorization mechanisms to prevent similar vulnerabilities in the future.

Patching and Updates

Ensure all software components, including OAuth2-Proxy and related dependencies, are regularly patched and updated to mitigate security risks.