A kube-apiserver security update has been released for Arch Linux.

ASA-202106-29: kube-apiserver: insufficient validation

Arch Linux Security Advisory ASA-202106-29
=========================================
Severity: Low
Date : 2021-06-09
CVE-ID : CVE-2021-25737
Package : kube-apiserver
Type : insufficient validation
Remote : Yes
Link :   https://security.archlinux.org/AVG-1970

Summary
======
The package kube-apiserver before version 1.21.1-1 is vulnerable to
insufficient validation.

Resolution
=========
Upgrade to 1.21.1-1.

# pacman -Syu "kube-apiserver>=1.21.1-1"

The problem has been fixed upstream in version 1.21.1.

Workaround
=========
To mitigate this vulnerability without upgrading kube-apiserver, you
can create a validating admission webhook that prevents EndpointSlices
with endpoint addresses in the 127.0.0.0/8 and 169.254.0.0/16 ranges.
If you have an existing admission policy mechanism (like OPA
Gatekeeper) you can create a policy that enforces this restriction.

Description
==========
A security issue was discovered in kube-apiserver before version 1.21.1
where a user may be able to redirect pod traffic to private networks on
a node. Kubernetes already prevents creation of Endpoint IPs in the
localhost or link-local range, but the same validation was not
performed on EndpointSlice IPs.

Impact
=====
A user could redirect pod traffic to private networks on a node.

References
=========
  https://github.com/kubernetes/kubernetes/issues/102106
  https://github.com/kubernetes/kubernetes/pull/101084
  https://github.com/kubernetes/kubernetes/commit/233c8d6eeef9e7a259c39dd1db096479044820ae
  https://security.archlinux.org/CVE-2021-25737