CVE-2021-25741 Explained : Impact and Mitigation

A security issue was discovered in Kubernetes where a user may be able to create a container with subpath volume mounts to access files & directories outside of the volume, including on the host filesystem.

Understanding CVE-2021-25741

This CVE identifies a vulnerability in Kubernetes that allows a user to exploit subpath volume mounts to gain unauthorized access to files on the host filesystem.

What is CVE-2021-25741?

The CVE-2021-25741 vulnerability in Kubernetes enables a user to create a container with subpath volume mounts to reach files and directories beyond the specified volume, potentially accessing sensitive information on the host filesystem.

The Impact of CVE-2021-25741

The impact of CVE-2021-25741 is rated as high with a base severity score of 8.8 out of 10 according to CVSS v3.1 metrics. This vulnerability can lead to unauthorized access to confidential data, compromise integrity, and disrupt system availability.

Technical Details of CVE-2021-25741

This section provides technical details regarding the vulnerability in question.

Vulnerability Description

The vulnerability allows a malicious user to manipulate subpath volume mounts in Kubernetes, breaching the container's isolation and gaining access to files outside of the designated volume.

Affected Systems and Versions

Kubernetes versions up to and including 1.22.1 are impacted by this vulnerability when utilizing custom versions specified with subpath volume mounts.

Exploitation Mechanism

By creating a container with carefully crafted subpath volume mounts, an attacker can traverse the filesystem and access sensitive information stored on the host.

Mitigation and Prevention

To safeguard your systems from CVE-2021-25741, consider the following mitigation strategies.

Immediate Steps to Take

Update Kubernetes to versions 1.19.15, 1.20.11, 1.21.5, or later that contain fixes for this vulnerability.
Regularly monitor container activities to detect any unauthorized access attempts.

Long-Term Security Practices

Implement least privilege access controls to restrict container permissions.
Conduct regular security audits to identify and address any potential vulnerabilities in your Kubernetes environment.

Patching and Updates

Stay informed about security advisories and updates from the Kubernetes project to apply patches promptly and enhance system security.