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Weave CNI password is not configured when a cluster is created from an RKE template

Moderate
maxsokolovsky published GHSA-vrph-m5jj-c46c May 24, 2022

Package

Rancher (Rancher)

Affected versions

Up to and including 2.5.13 and 2.6.4

Patched versions

2.5.14, 2.6.5 and later releases

Description

Impact

This vulnerability only affects customers using Weave CNI (Container Network Interface) when configured through RKE templates.

A flaw was discovered in Rancher versions from 2.5.0 up to and including 2.5.13 and from 2.6.0 up to and including 2.6.4, where a UI (user interface) issue with RKE templates does not include a value for the Weave password when Weave is chosen as the CNI.

If a cluster is created based on the mentioned template and Weave is configured as the CNI, no password will be created for network encryption in Weave, therefore network traffic in the cluster will be sent unencrypted.

This issue does not happen when a cluster, with Weave configured as CNI, is created without using an RKE template.

The impact of this vulnerability is higher when nodes on the cluster are on different locations and communicate with one another through the Internet, where monitoring (sniffing) of the network traffic by third-party entities can be more easily achieved.

Patches

Patched versions include releases 2.5.14, 2.6.5 and later versions of Rancher. Besides upgrading to a Rancher patched version, the workarounds listed below must be applied in order for Weave to properly encrypt the network traffic.

Workarounds

  1. A manual password can be set in Weave by directly editing Weave's DaemonSet on the affected cluster to add the WEAVE_PASSWORD environment variable together with the a value for the password.
$ kubectl -n kube-system edit ds weave-net
<snipped>
      containers:
      - command:
        - /home/weave/launch.sh
        env:
        - name: INIT_CONTAINER
          value: "true"
        - name: HOSTNAME
          valueFrom:
            fieldRef:
              apiVersion: v1
              fieldPath: spec.nodeName
        - name: IPALLOC_RANGE
          value: <IP allocation range>
        - name: WEAVE_PASSWORD
          value: "insert strong secret password here"
        image: <Weave image>
<snipped>
  1. A new RKE template revision must be created in order to properly generate the Weave password on new clusters.

Notes

  1. In order to provide protection against brute-force attacks, that might break the network encryption, a strong password must be generated for the workaround. Weave's documentation provides recommendations for generating a strong password.

  2. Manually generating the password for the workaround is only needed on affected versions of Rancher. This step is not needed when creating new RKE templates on patched versions of Rancher.

For more information

If you have any questions or comments about this advisory:

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

CVE ID

CVE-2022-21951

Weaknesses