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Security Bulletin: IBM Cloud Kubernetes Service is affected by a privilege escalation vulnerability in runc

Security Bulletin


IBM Cloud Kubernetes Service is affected by a security vulnerability in runc which could allow an attacker that is authorized to run a process as root inside a container to execute arbitrary commands with root privileges on the container’s host system.

Vulnerability Details

CVE-ID: CVE-2019-5736
Description: Runc could allow a local attacker to execute arbitrary commands on the system, cause by the improper handling of system file descriptors when running containers. An attacker could exploit this vulnerability using a malicious container to overwrite the contents of the host runc binary and execute arbitrary commands with root privileges on the host system.
CVSS Base Score: 7.7
CVSS Temporal Score: for more information
CVSS Environmental Score*: Undefined
CVSS Vector: (CVSS:3.0/AV:L/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H)

Affected Products and Versions

All versions of IBM Cloud Kubernetes Service are impacted.

Authenticated users on all versions that are authorized to run a process as root (UID 0) inside a container can exploit the vulnerability in runc. This can be done by running a container with a malicious image, or by any other means by which commands can be executed in a container, for example, kubectl exec. This exploit enables a malicious user to gain root privileges on the host running the container. Containers that cannot run processes as root are not exploitable.

To help mitigate this vulnerability, you are highly encouraged to Configure pod security policies in your cluster to prevent container processes from running as root.


Updates for IBM Cloud Kubernetes Service cluster worker nodes at versions 1.10 and later are available that fix this vulnerability.  Customers must update their worker nodes 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 version:

ibmcloud ks workers --cluster <cluster name or ID>
If the Kubernetes version is at one of the following patch levels or later the cluster worker node update has completed successfully:


Customers running IBM Cloud Kubernetes Service clusters at versions 1.7, 1.8 or 1.9 must upgrade their affected clusters to version 1.10. See Updating clusters for details on upgrading the cluster master and worker nodes.

Customers running IBM Cloud Kubernetes Service clusters at version 1.5 must create a new cluster and migrate their apps to it.

Note: IBM Cloud Kubernetes Service versions 1.5, 1.7, 1.8 and 1.9 are no longer supported.  See the IBM Cloud Kubernetes Service Version information and update actions documentation for more information about Kubernetes versions and version support policies.

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*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.


According to the Forum of Incident Response and Security Teams (FIRST), the Common Vulnerability Scoring System (CVSS) is an "industry open standard designed to convey vulnerability severity and help to determine urgency and priority of response." IBM PROVIDES THE CVSS SCORES ""AS IS"" WITHOUT WARRANTY OF ANY KIND, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. CUSTOMERS ARE RESPONSIBLE FOR ASSESSING THE IMPACT OF ANY ACTUAL OR POTENTIAL SECURITY VULNERABILITY. In addition to other efforts to address potential vulnerabilities, IBM periodically updates the record of components contained in our product offerings. As part of that effort, if IBM identifies previously unidentified packages in a product/service inventory, we address relevant vulnerabilities regardless of CVE date. Inclusion of an older CVEID does not demonstrate that the referenced product has been used by IBM since that date, nor that IBM was aware of a vulnerability as of that date. We are making clients aware of relevant vulnerabilities as we become aware of them. "Affected Products and Versions" referenced in IBM Security Bulletins are intended to be only products and versions that are supported by IBM and have not passed their end-of-support or warranty date. Thus, failure to reference unsupported or extended-support products and versions in this Security Bulletin does not constitute a determination by IBM that they are unaffected by the vulnerability. Reference to one or more unsupported versions in this Security Bulletin shall not create an obligation for IBM to provide fixes for any unsupported or extended-support products or versions.

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Document Information

Modified date:
18 February 2019