CVE-2021-41254 Privilege escalation to cluster admin on multi-tenant environments

2021-11-1217:45:10

CWE-78

GitHub_M

www.cve.org

kustomize-controller

kubernetes

privilege escalation

multi-tenant

cluster admin

cve-2021-41254

security vulnerability

flux kustomization

validation webhook

gatekeeper opa

kyverno

CVSS3

8.8

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

HIGH

Availability Impact

HIGH

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

AI Score

9.2

Confidence

High

EPSS

0.003

Percentile

70.3%

JSON

kustomize-controller is a Kubernetes operator, specialized in running continuous delivery pipelines for infrastructure and workloads defined with Kubernetes manifests and assembled with Kustomize. Users that can create Kubernetes Secrets, Service Accounts and Flux Kustomization objects, could execute commands inside the kustomize-controller container by embedding a shell script in a Kubernetes Secret. This can be used to run kubectl commands under the Service Account of kustomize-controller, thus allowing an authenticated Kubernetes user to gain cluster admin privileges. In affected versions multitenant environments where non-admin users have permissions to create Flux Kustomization objects are affected by this issue. This vulnerability was fixed in kustomize-controller v0.15.0 (included in flux2 v0.18.0) released on 2021-10-08. Starting with v0.15, the kustomize-controller no longer executes shell commands on the container OS and the kubectl binary has been removed from the container image. To prevent the creation of Kubernetes Service Accounts with secrets in namespaces owned by tenants, a Kubernetes validation webhook such as Gatekeeper OPA or Kyverno can be used.

CNA Affected

[
  {
    "product": "kustomize-controller",
    "vendor": "fluxcd",
    "versions": [
      {
        "status": "affected",
        "version": "< 0.15.0"
      }
    ]
  }
]