CVE-2020-14386

Description

A flaw was found in the Linux kernel. Memory corruption can be exploited to gain root privileges from unprivileged processes. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.

Statement

Only local users with CAP_NET_RAW capability enabled can trigger this issue.

For OpenShift Container Platform 4, pods in the default restricted SCC are granted CAP_NET_RAW by default. An attacker can exploit this if they can run arbitrary container images on the target cluster.

Mitigation

If the CAP_NET_RAW capability disabled by default (which is true for Red Hat Enterprise Linux), then only a privileged user can trigger this bug. The mitigation is to disable CAP_NET_RAW capability for regular users and for executables.

On Red Hat Enterprise Linux 8 CAP_NET_RAW capability can be also gained by exploiting unprivileged user namespaces. The mitigation is to disable unprivileged user namespaces by setting user.max_user_namespaces to 0:

# echo "user.max_user_namespaces=0" > /etc/sysctl.d/userns.conf
# sysctl -p /etc/sysctl.d/userns.conf

OpenShift Container Platform 4.5 and 4.4 this can be mitigated by removing `CAP_NET_RAW` from the default cri-o capabilities provided to pods (NOTE: This may prevent `ping` from working in unprivileged pods. This fix has not been validated for OpenShift 4.3 or below):

apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: worker
  name: 50-reset-crio-capabilities
spec:
  config:
    ignition:
      version: 2.2.0
    storage:
      files:
      - contents:
          source: data:text/plain;charset=utf-8;base64,W2NyaW8ucnVudGltZV0KZGVmYXVsdF9jYXBhYmlsaXRpZXMgPSBbCiAgICAiQ0hPV04iLAogICAgIkRBQ19PVkVSUklERSIsCiAgICAiRlNFVElEIiwKICAgICJGT1dORVIiLAogICAgIlNFVEdJRCIsCiAgICAiU0VUVUlEIiwKICAgICJTRVRQQ0FQIiwKICAgICJORVRfQklORF9TRVJWSUNFIiwKICAgICJTWVNfQ0hST09UIiwKICAgICJLSUxMIiwKXQo=
        filesystem: root
        mode: 0644
        path: /etc/crio/crio.conf.d/reset-crio-capabilities.conf

Create this MachineConfig object via e.g. `oc apply`. More information about MachineConfig can be found here:
https://github.com/openshift/machine-config-operator
https://docs.openshift.com/container-platform/4.5/architecture/architecture-rhcos.html

In order to monitor the rollout of this change, use `oc describe machineconfigpool/worker`.

Check for any pods which start to crash after this is applied; they may need to be adjusted request `CAP_NET_RAW` explicitly. More information:
https://kubernetes.io/docs/tasks/configure-pod-container/security-context/#set-capabilities-for-a-container
https://docs.openshift.com/container-platform/4.5/authentication/managing-security-context-constraints.html

Common Vulnerability Scoring System (CVSS) Score Details

Info alert:Important note

CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).

CVSS v3 Score Breakdown

Red HatNVDcve.org
Base Score7.87.8N/A
Attack VectorLocalLocalN/A
Attack ComplexityLowLowN/A
Privileges RequiredLowLowN/A
User InteractionNoneNoneN/A
ScopeUnchangedUnchangedN/A
ConfidentialityHighHighN/A
Integrity ImpactHighHighN/A
Availability ImpactHighHighN/A

Vector

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

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

Red Hat CVSS v3 Score Explanation

While PR:H is technically correct because of the CAP_NET_RAW capability requirement, unprivileged users on the system with unprivileged user namespaces enabled (this seems to be default among distributions) can grant themselves CAP_NET_RAW capability easily, so in practice, it's PR:L.

Understanding the Weakness (CWE)

CWE-786

Confidentiality

Technical Impact: Read Memory

For an out-of-bounds read, the attacker may have access to sensitive information. If the sensitive information contains system details, such as the current buffer's position in memory, this knowledge can be used to craft further attacks, possibly with more severe consequences.

Integrity,Availability

Technical Impact: Modify Memory; DoS: Crash, Exit, or Restart

Out of bounds memory access will very likely result in the corruption of relevant memory, and perhaps instructions, possibly leading to a crash.

Integrity

Technical Impact: Modify Memory; Execute Unauthorized Code or Commands

If the corrupted memory can be effectively controlled, it may be possible to execute arbitrary code. If the corrupted memory is data rather than instructions, the system will continue to function with improper changes, possibly in violation of an implicit or explicit policy.

Acknowledgements

Red Hat would like to thank Or Cohen (paloaltonetworks.com) for reporting this issue.

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