Security Bulletin: IBM Cloud Kubernetes Service is affected by Kubernetes API server security vulnerabilities (CVE-2023-39325 and CVE-2023-44487)

Summary

IBM Cloud Kubernetes Service is affected by security vulnerabilities in the Kubernetes API server that may allow a denial of service attack from unauthenticated clients (CVE-2023-39325 and CVE-2023-44487).

Vulnerability Details

CVEID: CVE-2023-39325

Description: A malicious HTTP/2 client which rapidly creates requests and immediately resets them can cause excessive server resource consumption. While the total number of requests is bounded by the http2.Server.MaxConcurrentStreams setting, resetting an in-progress request allows the attacker to create a new request while the existing one is still executing. With the fix applied, HTTP/2 servers now bound the number of simultaneously executing handler goroutines to the stream concurrency limit (MaxConcurrentStreams). New requests arriving when at the limit (which can only happen after the client has reset an existing, in-flight request) will be queued until a handler exits. If the request queue grows too large, the server will terminate the connection. This issue is also fixed in golang.org/x/net/http2 for users manually configuring HTTP/2. The default stream concurrency limit is 250 streams (requests) per HTTP/2 connection. This value may be adjusted using the golang.org/x/net/http2 package; see the Server.MaxConcurrentStreams setting and the ConfigureServer function.
CVSS Base Score: 7.5
CVSS Temporal Score: <https://exchange.xforce.ibmcloud.com/vulnerabilities/268645&gt; for more information
CVSS Vector: (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

CVEID: CVE-2023-44487
Description: The HTTP/2 protocol is vulnerable to a denial of service, caused by an uncontrolled server resource consumption flaw, because request cancellation can reset many streams quickly, as exploited in the wild in August through October 2023. By sending specially crafted requests using HTTP/2 client, a remote attacker could exploit this vulnerability to cause a denial of service condition.
CVSS Base Score: 7.5
CVSS Temporal Score: <https://exchange.xforce.ibmcloud.com/vulnerabilities/268645&gt; for more information
CVSS Vector: (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Affected Products and Versions

IBM Cloud Kubernetes Service 1.28.0-1.28.3
IBM Cloud Kubernetes Service 1.27.0-1.27.7
IBM Cloud Kubernetes Service 1.26.0-1.26.10
IBM Cloud Kubernetes Service 1.25.0-1.25.15
IBM Cloud Kubernetes Service 1.5-1.24

Remediation/Fixes

Updates for IBM Cloud Kubernetes Service clusters at version 1.25 or later are available that fix this vulnerability. IBM Cloud Kubernetes Service will attempt to automatically apply the fix to your cluster master. There is no need to update cluster worker nodes for this vulnerability.

To verify your clusters are no longer exposed to this vulnerability, use the following IBM Cloud CLI command to confirm your cluster master versions:

ibmcloud ks clusters

If your cluster masters are at one of the following versions or later, they are no longer exposed to this vulnerability:

1.28.4
1.27.8
1.26.11
1.25.16

If one or more of your clusters has not had its master automatically updated then use the following IBM Cloud CLI command to complete the cluster master update, replacing 1.## with the target version.

ibmcloud ks cluster master update --cluster <cluster name or ID> --version 1.##

Customers running IBM Cloud Kubernetes Service clusters at version 1.23 or 1.24 must upgrade to version 1.25. Please review the documentation before starting an upgrade since additional actions may be required.

Customers running IBM Cloud Kubernetes Service clusters at version 1.22 or earlier must create a new cluster and deploy their apps to the new cluster.

IBM Cloud Kubernetes Service versions 1.23 and earlier are no longer supported and version 1.24 is deprecated with end of support tentatively scheduled for 14 December 2023. See the IBM Cloud Kubernetes Service version information and update actions documentation for more information about Kubernetes versions and version support policies.