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

Quick assessment

Affected
fluxcd kustomize-controller
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

kustomize-controller是一个 Kubernetes 操作员，专门为使用 Kubernetes 清单定义并使用 Kustomize 组装的基础设施和工作负载运行持续交付管道。 kustomize-controlle 0.15.0之前版本存在操作系统命令注入漏洞，经过身份验证的攻击者可以通过该漏洞获得集群管理员权限。

CVSS 8.8 · High EPSS 1.77% · P76

Possible ATT&CK Techniques 1 AI

T1651 · Cloud Administration Command
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I. Basic Information for CVE-2021-41254

Vulnerability Information
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Vulnerability Title
Privilege escalation to cluster admin on multi-tenant environments
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
OS命令中使用的特殊元素转义处理不恰当(OS命令注入)
Source: CVE Program / CVE List V5
Vulnerability Title
kustomize-controller 操作系统命令注入漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
kustomize-controller是一个 Kubernetes 操作员，专门为使用 Kubernetes 清单定义并使用 Kustomize 组装的基础设施和工作负载运行持续交付管道。 kustomize-controlle 0.15.0之前版本存在操作系统命令注入漏洞，经过身份验证的攻击者可以通过该漏洞获得集群管理员权限。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
fluxcd kustomize-controller < 0.15.0 -

II. Public POCs for CVE-2021-41254

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III. Intelligence Information for CVE-2021-41254

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Vendor Advisories for CVE-2021-41254 (1)

IV. Related Vulnerabilities

Same vendor: fluxcd
Same weakness: CWE-78

V. Comments for CVE-2021-41254

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