CVE-2020-8562: Bypass of Kubernetes API Server proxy TOCTOU
First published: Tue Feb 01 2022(Updated: )
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.
Credit: jordan@liggitt.net jordan@liggitt.net
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Kubernetes Kubernetes | <=1.18.18 | |
| Kubernetes Kubernetes | >=1.19.0<=1.19.10 | |
| Kubernetes Kubernetes | >=1.20.0<=1.20.6 | |
| Kubernetes Kubernetes | =1.21.0 | |
| go/k8s.io/kubernetes | <=1.18.19 | |
| go/k8s.io/kubernetes | >=1.19.0<=1.19.11 | |
| go/k8s.io/kubernetes | >=1.20.0<=1.20.7 | |
| go/k8s.io/kubernetes | >=1.21.0<=1.21.1 |
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Reference Links
- https://github.com/kubernetes/kubernetes/issues/101493
- https://groups.google.com/g/kubernetes-security-announce/c/-MFX60_wdOY
- https://security.netapp.com/advisory/ntap-20220225-0002/
- https://nvd.nist.gov/vuln/detail/CVE-2020-8562
- https://github.com/kubernetes/kubernetes/issues/101493#issuecomment-2272095629
- https://security.netapp.com/advisory/ntap-20220225-0002
- https://github.com/advisories/GHSA-qh36-44jv-c8xj (Advisory)
Frequently Asked Questions
What is CVE-2020-8562?
CVE-2020-8562 is a vulnerability in Kubernetes that allows proxied connections to access link-local or localhost networks.
How severe is CVE-2020-8562?
CVE-2020-8562 has a severity value of 3.1, which is considered low.
Which versions of Kubernetes are affected by CVE-2020-8562?
Kubernetes versions 1.18.18, 1.19.0 to 1.19.10, 1.20.0 to 1.20.6, and 1.21.0 are affected by CVE-2020-8562.
How can I mitigate CVE-2020-8562?
To mitigate CVE-2020-8562, ensure that Kubernetes is configured to prevent proxied connections from accessing link-local or localhost networks.
Where can I find more information about CVE-2020-8562?
You can find more information about CVE-2020-8562 in the following references: [Reference 1](https://github.com/kubernetes/kubernetes/issues/101493), [Reference 2](https://groups.google.com/g/kubernetes-security-announce/c/-MFX60_wdOY), [Reference 3](https://security.netapp.com/advisory/ntap-20220225-0002/)
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