CVE-2020-8562 Bypass of Kubernetes API Server proxy TOCTOU

2021-05-0400:00:00

CWE-367

kubernetes

www.cve.org

2.2 Low

CVSS3

Attack Vector

NETWORK

Attack Complexity

HIGH

Privileges Required

HIGH

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

LOW

Integrity Impact

NONE

Availability Impact

NONE

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

5.2 Medium

AI Score

Confidence

Low

0.001 Low

EPSS

Percentile

41.5%

JSON

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.

CNA Affected

[
  {
    "product": "Kubernetes",
    "vendor": "Kubernetes",
    "versions": [
      {
        "lessThanOrEqual": "v1.18.18",
        "status": "affected",
        "version": "unspecified",
        "versionType": "custom"
      },
      {
        "lessThan": "unspecified",
        "status": "unknown",
        "version": "next of v1.18.18",
        "versionType": "custom"
      },
      {
        "lessThanOrEqual": "v1.19.10",
        "status": "affected",
        "version": "unspecified",
        "versionType": "custom"
      },
      {
        "lessThan": "unspecified",
        "status": "unknown",
        "version": "next of v1.19.10",
        "versionType": "custom"
      },
      {
        "lessThanOrEqual": "v1.20.6",
        "status": "affected",
        "version": "unspecified",
        "versionType": "custom"
      },
      {
        "lessThan": "unspecified",
        "status": "unknown",
        "version": "next of v1.20.6",
        "versionType": "custom"
      },
      {
        "lessThanOrEqual": "v1.21.0",
        "status": "affected",
        "version": "unspecified",
        "versionType": "custom"
      },
      {
        "lessThan": "unspecified",
        "status": "unknown",
        "version": "next of v1.21.0",
        "versionType": "custom"
      }
    ]
  }
]