CVE-2021-22538 : Security Advisory and Response

A privilege escalation vulnerability impacting the Google Exposure Notification Verification Server (versions prior to 0.23.1) allows an attacker to create a user with higher privileges by exploiting insufficient permission checks.

Understanding CVE-2021-22538

This CVE describes a privilege escalation vulnerability in the RBAC system of Google's Exposure Notifications Verification Server.

What is CVE-2021-22538?

CVE-2021-22538 is a security flaw in the Google Exposure Notification Verification Server, allowing an attacker to create a user with elevated permissions due to inadequate permission validation.

The Impact of CVE-2021-22538

The vulnerability poses a medium-severity risk, with low impacts on confidentiality, integrity, and availability.

Technical Details of CVE-2021-22538

The following technical details outline the vulnerability's specifics.

Vulnerability Description

The flaw enables an attacker with UserWrite permissions to craft a request or use a malicious proxy to create a user with higher privileges than their own.

Affected Systems and Versions

All platforms running Google Exposure Notification Verification Server prior to version 0.23.1 are impacted.

Exploitation Mechanism

The vulnerability arises from insufficient checks on permissions, allowing the attacker to bypass validation and escalate privileges.

Mitigation and Prevention

To address CVE-2021-22538, consider the following mitigation strategies.

Immediate Steps to Take

Upgrade to version 0.23.1 or above to mitigate the vulnerability.
Monitor user creation events for anomalies.

Long-Term Security Practices

Regularly review and update access control policies.
Implement logging and monitoring for unusual user activities.

Patching and Updates

Stay informed about security advisories and promptly apply patches and updates released by Google.