Security Bulletin: IBM Cloud Kubernetes Service is affected by a Kubernetes kubelet security vulnerability (CVE-2020-8557)

Summary

IBM Cloud Kubernetes Service is affected by a security vulnerability in the Kubernetes kubelet that could result in the denial of service of a node (CVE-2020-8557)

Vulnerability Details

CVEID: CVE-2020-8557

Description: Kubernetes kubelet is vulnerable to a denial of service, caused by an issue with not including the /etc/hostsfile file by the kubelet eviction manager when calculating ephemeral storage usage. By writing a large amount of data to the /etc/hostsfile, a local authenticated attacker could exploit this vulnerability to fill the storage space of the node and cause the node to fail.
CVSS Base Score: 5.5
CVSS Temporal Score: https://exchange.xforce.ibmcloud.com/vulnerabilities/185301 for more information
CVSS Vector: (CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)

Affected Products and Versions

IBM Cloud Kubernetes Service 1.18.0-1.18.5
IBM Cloud Kubernetes Service 1.17.0-1.17.8
IBM Cloud Kubernetes Service 1.16.0-1.16.12
IBM Cloud Kubernetes Service 1.5-1.15

Remediation/Fixes

Updates for IBM Cloud Kubernetes Service cluster worker nodes at versions 1.16 or later are available that fix this vulnerability. Customers must update worker nodes created before the fix was available to address the vulnerability. See updating worker nodes for details on updating worker nodes. To verify your cluster worker nodes have been updated, use the following IBM Cloud CLI command to confirm the currently running versions:

ibmcloud ks workers --cluster <cluster name or ID>

If the versions are at one of the following patch levels or later, the cluster worker nodes have the fix:

1.18.6
1.17.9
1.16.13

Customers running IBM Cloud Kubernetes Service clusters at version 1.14 or 1.15 must upgrade to version 1.16. Please review the documentation before starting an upgrade since additional actions may be required.

Customers running IBM Cloud Kubernetes Service clusters at version 1.13 or earlier must create a new cluster and deploy their apps to the new cluster.

IBM Cloud Kubernetes Service versions 1.14 and earlier are no longer supported, and version 1.15 is deprecated. See the IBM Cloud Kubernetes Service Version information and update actions documentation for more information about Kubernetes versions and version support policies.

Workarounds and Mitigations

You can mitigate this vulnerability by Configuring pod security policies and restricting RBAC in order to limit access for authorized users as is detailed in the Kubernetes security advisory CVE-2020-8557: Node disk DOS by writing to container /etc/hosts.

Monitor IBM Cloud Status for Future Security Bulletins

Monitor the security notifications on the IBM Cloud Status page to be advised of future security bulletins.

References

Complete CVSS v3 Guide
On-line Calculator v3

Off

Kubernetes Security Announcement for CVE-2020-8557

Related Information

IBM Secure Engineering Web Portal
IBM Product Security Incident Response Blog

*The CVSS Environment Score is customer environment specific and will ultimately impact the Overall CVSS Score. Customers can evaluate the impact of this vulnerability in their environments by accessing the links in the Reference section of this Security Bulletin.

Disclaimer

Review the IBM security bulletin disclaimer and definitions regarding your responsibilities for assessing potential impact of security vulnerabilities to your environment.

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