[Bug] Security Capabilites must omit the CAP prefix which is required by Kyverno policies

[StraysWonderland]

Kyverno Version

1.11

Kubernetes Version

1.26

Kubernetes Platform

EKS

Description

We have implemented a subset of the best practices policies on our aks cluster.
The issue I'm facing is related to the require-drop-cap-net-raw policy which can be found here within the kyverno policies repository

However this policy does only recognize a pod as passing the policy if the capability section is defined as:

securityContext:
  capabilities:
    drop:
      - CAP_NET_RAW

so with the CAP prefix

According to the official kubernetes documentation however, these capabilities should omit the CAP prefix as can be seen here:

And the problem is that kyverno does not seem to recognize resources dropping the capabilities in this manner:

securityContext:
  capabilities:
    drop: ["NET_RAW"]

Ive done a bit of testing on some pods and it seems that pods with the CAP_NET_RAW definition, tough passing the kyverno policy, are not actually dropping the security capabilities while pods with the NET_RAW definition fail kyverno but are correctly dropping the security capability.

Ive also visualised how kyverno fails/passes these different definitions in the kyverno playground via this test using the official kyverno policy and two pods with the different capability syntax.

And the playground test also shows that
CAP_NET_RAW is passing while
NET_RAW is failing

Steps to reproduce

1. Implement the require-cap-net-raw policy - on audit mode ideally
2. deploy a pod that specifies securityContext capabilities drop: CAP_NET_RAW
3. deploy a second pod with the securityContext capabilities drop: NET_RAW

Expected behavior

Kyverno should allow the 2nd pod with NET_RAW syntax as according to kubernetes this is the correct way to drop the capability.
And likely not accept the CAP_NET_RAW definition as this does not actually seem to achieve what it should within the container.

Screenshots

No response

Kyverno logs

No response

Slack discussion

No response

Troubleshooting

• I have read and followed the documentation AND the troubleshooting guide.
• I have searched other issues in this repository and mine is not recorded.

[epasham]

Can we modify the policy to support both CAP_NET_RAW and NET_RAW capabilities instead of omiting CAP prefix

[StraysWonderland]

that would be an option.
However; My concern is that when specifying CAP_NET_RAW on your kubernetes resources, the pod still has the capabilities that should be dropped.
So while kyverno will say that all is fine and secure; the pod is still vulnerable to i.e. spoofing attacks as pods still have access to the NET_RAW capabilities.

My tests indicate that behaviour but I think ideally someone would need to confirm my suspicion to be sure about this.
If my suspicion is incorrect then allowing both is a suitable solution I believe

[epasham]

I have seen in some deployment manifests CAP_NET_RAW is used. It might be Operating system specific. For now, good option is to allow both CAP_NET_RAW and NET_RAW.

[epasham]

The changes are done and tested. will be submitting the pull request shortly.

[epasham]

PR is submitted #1168