ArchLinux: 202106-29: kube-apiserver: insufficient validation
Summary
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.
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.
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
Workaround
To mitigate this vulnerability without upgrading kube-apiserver, youcan create a validating admission webhook that prevents EndpointSliceswith 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 OPAGatekeeper) you can create a policy that enforces this restriction.