CVE-2020-8557 : Vulnerability Insights and Analysis

Kubernetes node disk Denial of Service by writing to container /etc/hosts

Understanding CVE-2020-8557

This CVE involves a vulnerability in the Kubernetes kubelet component that affects various versions of Kubernetes.

What is CVE-2020-8557?

The Kubernetes kubelet component in versions 1.1-1.16.12, 1.17.0-1.17.8, and 1.18.0-1.18.5 does not consider disk usage by a pod writing to its /etc/hosts file. This oversight can lead to node failure if the pod fills the storage space by writing excessive data to the /etc/hosts file.

The Impact of CVE-2020-8557

The vulnerability has a CVSS base score of 5.5, indicating a medium severity issue. The attack complexity is low, but the availability impact is high. Although it does not affect confidentiality or integrity, it requires low privileges and has a local attack vector.

Technical Details of CVE-2020-8557

The following technical details provide insight into the vulnerability:

Vulnerability Description

The kubelet eviction manager in affected Kubernetes versions does not account for disk usage by pods writing to their /etc/hosts file, potentially leading to node failure due to storage space exhaustion.

Affected Systems and Versions

Kubernetes versions 1.1 to 1.16.12
Kubernetes versions 1.17.0 to 1.17.8
Kubernetes versions 1.18.0 to 1.18.5

Exploitation Mechanism

Pods writing a large amount of data to the /etc/hosts file can exhaust the storage space of the node, causing it to fail.

Mitigation and Prevention

To address CVE-2020-8557, consider the following steps:

Immediate Steps to Take

Monitor disk usage by pods and set limits to prevent excessive writes.
Regularly check node storage space to detect any anomalies.

Long-Term Security Practices

Implement least privilege access for pods to limit potential damage.
Keep Kubernetes clusters updated to patched versions to mitigate known vulnerabilities.

Patching and Updates

Apply patches provided by Kubernetes to fix the kubelet component's disk usage calculation.