CVE-2021-32724 : Exploit Details and Defense Strategies

A GitHub action called check-spelling, specifically versions earlier than 0.0.19, is vulnerable to a symlink attack leading to GITHUB_TOKEN leakage, potentially allowing unauthorized pushes and access to repository secrets.

Understanding CVE-2021-32724

This CVE involves the exposure of sensitive information due to a security vulnerability in the check-spelling GitHub action.

What is CVE-2021-32724?

The check-spelling GitHub action, when triggered on specific events, could be exploited by an attacker to expose the GITHUB_TOKEN. This token could then be used to push unauthorized commits and access confidential repository secrets.

The Impact of CVE-2021-32724

With a CVSS v3.1 base score of 9.9 (Critical), this vulnerability has a high confidentiality, integrity, and availability impact. It requires low privileges and no user interaction, affecting network scope with low attack complexity.

Technical Details of CVE-2021-32724

This section dives into the specifics of the vulnerability.

Vulnerability Description

The vulnerability allows an attacker to craft a malicious Pull Request triggering the exposure of the GITHUB_TOKEN, enabling unauthorized commits and access to repository secrets.

Affected Systems and Versions

Versions prior to 0.0.19 of the check-spelling GitHub action are affected by this vulnerability.

Exploitation Mechanism

By leveraging a symlink attack, an attacker can exploit the workflow to leak the GITHUB_TOKEN, bypassing approval processes and gaining unauthorized access.

Mitigation and Prevention

Protecting against this vulnerability requires immediate actions and long-term security practices.

Immediate Steps to Take

Users are advised to disable the workflow until all branches are fixed or set repository permissions to only allow specific actions. Updating affected workflows to the latest version is also crucial.

Long-Term Security Practices

Implement strict workflow permissions, review and verify all actions in use, and regularly monitor the Actions tab for any unauthorized activity.

Patching and Updates

Ensure that affected workflows are updated to the latest version of the check-spelling GitHub action. Verify actions running on repositories for unauthorized access.