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Authenticated user can gain unauthorized shell pod and kubectl access in the local cluster

High severity GitHub Reviewed Published Jan 25, 2023 in rancher/rancher • Updated Feb 7, 2023

Package

gomod github.com/rancher/rancher (Go)

Affected versions

>= 2.5.0, < 2.5.17
>= 2.6.0, < 2.6.10
>= 2.7.0, < 2.7.1

Patched versions

2.5.17
2.6.10
2.7.1

Description

Impact

An issue was discovered in Rancher where an authorization logic flaw allows an authenticated user on any downstream cluster to (1) open a shell pod in the Rancher local cluster and (2) have limited kubectl access to it. The expected behavior is that a user does not have such access in the Rancher local cluster unless explicitly granted.

This issue does not allow the user to escalate privileges in the local cluster directly (this would require another vulnerability to be exploited).

The security issue happens in two different ways:

  1. Shell pod access - This is when a user opens a shell pod in the Rancher UI to a downstream cluster that the user has permission to access. The web request can be intercepted using the browser's web inspector/network console or a proxy tool to change the shell's destination to the Rancher local cluster instead of the desired downstream cluster.

    • This flaw cannot be exploited to access a downstream cluster that the user has no permissions to.

    • The shell pod runs with a limited non-root user, reducing the severity of this issue. However, even as a non-root user, it is still possible download and run binaries inside the shell pod.

    • The blast radius of this issue can increase based on the configuration of the local cluster. For example:

      • If the local cluster has unlimited network access, e.g. to the Internet, the user can open a reverse network connection to the shell pod.

      • Or access the cloud metadata API of the underlying cloud infrastructure, where the user can extract the credentials associated with the local cluster and use them to interact with the cloud environment (this will be limited by the permissions granted to the cloud credentials in question).

      • Check further recommendations about liming access to the cloud metadata API in Rancher's security best practices.

  2. Kubectl access - When downloading the kubeconfig file of a downstream cluster that the user has access to, the server cluster address in the kubeconfig file can be changed to point to the Rancher local cluster instead of the intended downstream cluster.

    • This can also be achieved by crafting a kubeconfig using a Rancher token instead of using the kubeconfig from an active cluster.

    • This flaw cannot be exploited to access a downstream cluster that the user has no permissions to.

Notes:

  • Rancher local cluster means the cluster where Rancher is installed. It is named as local inside the list of clusters in the Rancher UI.
  • Audit logs in Rancher can be used to identify possible abuses of this issue, by tracking API requests to the user ID of the user that performed the action. API audit logs can be enabled as described in the documentation when set to level 1 or above.

Workarounds

There is no workaround or direct mitigation besides updating to a patched Rancher version.

Patches

Patched versions include releases 2.5.17, 2.6.10, 2.7.1 and later versions.

For more information

If you have any questions or comments about this advisory:

References

@macedogm macedogm published to rancher/rancher Jan 25, 2023
Published to the GitHub Advisory Database Jan 25, 2023
Reviewed Jan 25, 2023
Published by the National Vulnerability Database Feb 7, 2023
Last updated Feb 7, 2023

Severity

High

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
Low
Privileges required
Low
User interaction
None
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
Low

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:L/PR:L/UI:N/S:C/C:L/I:L/A:L

EPSS score

0.087%
(38th percentile)

CVE ID

CVE-2022-21953

GHSA ID

GHSA-g25r-gvq3-wrq7

Source code

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