CVSS Rating: Low (CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:L/I:N/A:N)

A security issue was discovered in Kubernetes where an authorized user may be able to access private networks on the Kubernetes control plane components. Kubernetes clusters are only affected if an untrusted user can create or modify Node objects and proxy to them, or an untrusted user can create or modify StorageClass objects and access KubeControllerManager logs.

This issue has been rated Low (CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:L/I:N/A:N) and assigned CVE-2020-8562.

As mitigations to a report from 2019 and CVE-2020-8555, Kubernetes attempts to prevent proxied connections from accessing link-local or localhost networks when making user-driven connections to Services, Pods, Nodes, or StorageClass service providers. As part of this mitigation Kubernetes does a DNS name resolution check and validates that response IPs are not in the link-local (169.254.0.0/16) or localhost (127.0.0.0/8) range. Kubernetes then performs a second DNS resolution without validation for the actual connection. If a non-standard DNS server returns different non-cached responses, a user may be able to bypass the proxy IP restriction and access private networks on the control plane.

Affected Versions:

All versions of Kubernetes are affected

Fixed Versions

There is no fix for this issue at this time.

Mitigations

If this issue affects your clusters’ control planes, you can use dnsmasq for name resolution and configure the min-cache-ttl and neg-ttl parameters to a low non-zero value to enforce cached replies for proxied connections.

Detection

This issue is not known to be directly detectable, but proxied calls will appear in the Kubernetes API Audit log. Kubernetes will respond with “address not allowed” when the validation successfully prevents a connection.

Acknowledgements

This vulnerability was reported by Javier Provecho (Telefonica).

/area security
/kind bug
/committee product-security
/triage accepted