Targeting this bug for next 2.6.z release.
We already have a bug targeted for release 4.9.0, https://bugzilla.redhat.com/show_bug.cgi?id=1985719


We need a back-port of this for 2.6.z, https://github.com/kubevirt/kubevirt/pull/6147

verify with build 
HCO:[v2.6.7-41]

step:
1. prepare a vm with guest agent installed
2. create unprivilege user with clusterrole
$ cat role.yaml
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: my-custom-rbac-role
  labels:
    kubevirt.io: ""
rules:
  - apiGroups:
      - subresources.kubevirt.io
    resources:
      - virtualmachineinstances/console
      - virtualmachineinstances/guestosinfo
    verbs:
      - get
  - apiGroups:
      - kubevirt.io
    resources:
      - virtualmachineinstances
      - virtualmachines
      - virtualmachineinstancepresets
      - virtualmachineinstancereplicasets
    verbs:
      - get
      - list
      - watch

3. login with unprivilege user 
$ oc whoami
redhat

4. check vm guest info
$ virtctl guestosinfo vm-rhel
{
  "guestAgentVersion": "6.1.0",
  "supportedCommands": [
    {
      "name": "guest-ssh-remove-authorized-keys",
      "enabled": true
    },
    {
      "name": "guest-ssh-add-authorized-keys",
      "enabled": true
    },
    {
      "name": "guest-ssh-get-authorized-keys",
      "enabled": true
    },
    {
      "name": "guest-get-devices"
    },
    {
      "name": "guest-get-osinfo",
      "enabled": true
    },
    {
      "name": "guest-get-timezone",
      "enabled": true
    },
    {
      "name": "guest-get-users",
      "enabled": true
    },
    {
      "name": "guest-get-host-name",
      "enabled": true
    },
    {
      "name": "guest-exec"
    },
    {
      "name": "guest-exec-status"
    },
    {
      "name": "guest-get-memory-block-info",
      "enabled": true
    },
    {
      "name": "guest-set-memory-blocks",
      "enabled": true
    },
    {
      "name": "guest-get-memory-blocks",
      "enabled": true
    },
    {
      "name": "guest-set-user-password",
      "enabled": true
    },
    {
      "name": "guest-get-fsinfo",
      "enabled": true
    },
    {
      "name": "guest-get-disks",
      "enabled": true
    },
    {
      "name": "guest-set-vcpus",
      "enabled": true
    },
    {
      "name": "guest-get-vcpus",
      "enabled": true
    },
    {
      "name": "guest-network-get-interfaces",
      "enabled": true
    },
    {
      "name": "guest-suspend-hybrid",
      "enabled": true
    },
    {
      "name": "guest-suspend-ram",
      "enabled": true
    },
    {
      "name": "guest-suspend-disk",
      "enabled": true
    },
    {
      "name": "guest-fstrim",
      "enabled": true
    },
    {
      "name": "guest-fsfreeze-thaw",
      "enabled": true
    },
    {
      "name": "guest-fsfreeze-freeze-list",
      "enabled": true
    },
    {
      "name": "guest-fsfreeze-freeze",
      "enabled": true
    },
    {
      "name": "guest-fsfreeze-status",
      "enabled": true
    },
    {
      "name": "guest-file-flush"
    },
    {
      "name": "guest-file-seek"
    },
    {
      "name": "guest-file-write"
    },
    {
      "name": "guest-file-read"
    },
    {
      "name": "guest-file-close"
    },
    {
      "name": "guest-file-open"
    },
    {
      "name": "guest-shutdown",
      "enabled": true
    },
    {
      "name": "guest-info",
      "enabled": true
    },
    {
      "name": "guest-set-time",
      "enabled": true
    },
    {
      "name": "guest-get-time",
      "enabled": true
    },
    {
      "name": "guest-ping",
      "enabled": true
    },
    {
      "name": "guest-sync",
      "enabled": true
    },
    {
      "name": "guest-sync-delimited",
      "enabled": true
    }
  ],
  "hostname": "vm-rhel",
  "os": {
    "name": "Red Hat Enterprise Linux",
    "kernelRelease": "4.18.0-343.el8.x86_64",
    "version": "8.6 (Ootpa)",
    "prettyName": "Red Hat Enterprise Linux 8.6 Beta (Ootpa)",
    "versionId": "8.6",
    "kernelVersion": "#1 SMP Thu Sep 16 18:45:53 EDT 2021",
    "machine": "x86_64",
    "id": "rhel"
  },
  "timezone": "EDT, -14400",
  "fsInfo": {
    "disks": [
      {
        "diskName": "vdb2",
        "mountPoint": "/boot/efi",
        "fileSystemType": "vfat",
        "usedBytes": 6006784,
        "totalBytes": 104634368
      },
      {
        "diskName": "vdb3",
        "mountPoint": "/",
        "fileSystemType": "xfs",
        "usedBytes": 2047205376,
        "totalBytes": 21357375488
      }
    ]
  }
}

move to verified.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (Low: OpenShift Virtualization 2.6.7 Images security and bug fix update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2021:3733