CVE-2020-25584 : Exploit Details and Defense Strategies

In FreeBSD 13.0-STABLE before n245118, 12.2-STABLE before r369552, 11.4-STABLE before r369560, 13.0-RC5 before p1, 12.2-RELEASE before p6, and 11.4-RELEASE before p9, a superuser inside a FreeBSD jail configured with the non-default allow.mount permission could cause a race condition between the lookup of ".." and remounting a filesystem, allowing access to filesystem hierarchy outside of the jail.

Understanding CVE-2020-25584

This CVE describes a Time-of-check Time-of-use Race Condition vulnerability in FreeBSD.

What is CVE-2020-25584?

A superuser within a FreeBSD jail with specific permissions could exploit a race condition, potentially leading to unauthorized access outside the jail.

The Impact of CVE-2020-25584

The vulnerability could allow a malicious actor to access the filesystem hierarchy beyond the confines of the FreeBSD jail, compromising system integrity and confidentiality.

Technical Details of CVE-2020-25584

This section provides detailed technical information about the vulnerability.

Vulnerability Description

The vulnerability arises due to a race condition between the lookup of ".." and filesystem remounting within a FreeBSD jail.

Affected Systems and Versions

Affected Versions: FreeBSD 12.2-RELEASE before p6, 11.4-RELEASE before p9
Systems: FreeBSD 13.0-STABLE, 12.2-STABLE, 11.4-STABLE, 13.0-RC5

Exploitation Mechanism

The exploitation involves manipulating the filesystem remounting process within a FreeBSD jail to gain unauthorized access.

Mitigation and Prevention

Protect your systems from CVE-2020-25584 with the following measures.

Immediate Steps to Take

Apply the provided patches promptly to mitigate the vulnerability.
Review and adjust jail configurations to limit superuser permissions.

Long-Term Security Practices

Regularly update FreeBSD systems to the latest stable releases.
Implement the principle of least privilege to restrict superuser access within jails.

Patching and Updates

Stay informed about security advisories from FreeBSD.
Apply security patches and updates as soon as they are available.