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GHSA-g25r-gvq3-wrq7 CVE-2022-21953

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

High Go
Severity
7.4 / 10
High · CVSS 3.1
Exploit chance (EPSS)
0.47%
Chance of exploitation in the next 30 days. Higher than 40.64% of scored vulnerabilities.
Known exploited
No
Not in CISA's catalog
Weakness
CWE-284 Improper Access Control
CWE-285 Improper Authorization
CWE-862 Missing Authorization
Fix
2.5.17
Upgrade github.com/rancher/rancher to this version or later

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:

Affected versions

Go

PackageVulnerableFixed in
github.com/rancher/rancher
>= 2.5.0, < 2.5.17
2.5.17
github.com/rancher/rancher
>= 2.6.0, < 2.6.10
2.6.10
github.com/rancher/rancher
>= 2.7.0, < 2.7.1
2.7.1

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

github.com/rancher/rancher Go → 2.5.17

go
go get github.com/rancher/rancher@v2.5.17 && go mod tidy

Severity breakdown

CVSS 3.1 7.4

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

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

Weakness

CWE-284: Improper Access Control

The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.

How to prevent it
  • Architecture and Design, Operation: Very carefully manage the setting, management, and handling of privileges. Explicitly manage trust zones in the software.
  • Architecture and Design: Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.

CWE-285: Improper Authorization

The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action.

How to prevent it
  • Architecture and Design: Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries. Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
  • Architecture and Design: Ensure that you perform access control checks related to your business logic. These checks may be different than the access control checks that you apply to more generic resources such as files, connections, processes, memory, and database records. For example, a database may restrict access for medical records to a specific database user, but each record might only be intended to be accessible to the patient and the patient's doctor.
  • Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
  • Architecture and Design: For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page. One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.
  • System Configuration, Installation: Use the access control capabilities of your operating system and server environment and define your access control lists accordingly. Use a "default deny" policy when defining these ACLs.

CWE-862: Missing Authorization

The product does not perform an authorization check when an actor attempts to access a resource or perform an action.

How to prevent it
  • Architecture and Design: Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) [REF-229] to enforce the roles at the appropriate boundaries. Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
  • Architecture and Design: Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records. For example, a database may restrict access for medical records to a specific database user, but each record might only be intended to be accessible to the patient and the patient's doctor [REF-7].
  • Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
  • Architecture and Design: For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page. One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.
  • System Configuration, Installation: Use the access control capabilities of your operating system and server environment and define your access control lists accordingly. Use a "default deny" policy when defining these ACLs.

References

Advisories

Packages

Other links

Timeline

  1. Published
  2. Last updated by the source
  3. Latest EPSS score
AdvisorySeverityWhy it's related
GHSA-4j6x-2764-m8gh
Rancher has over-inclusive team membership expansion in GitHub App authentication provider
High Also affects github.com/rancher/rancher
GHSA-vx8h-4prv-g744
Rancher has Privilege Escalation from Project Owner to Host
High Also affects github.com/rancher/rancher
GHSA-mhc6-2gfq-xx62
Rancher vulnerable to command injection through unsanitized YAML parameter
Critical Also affects github.com/rancher/rancher
GHSA-5v3h-x4wf-5c35
Rancher Extensions have arbitrary file access via path traversal
High Also affects github.com/rancher/rancher
GHSA-gqf8-rvrh-g7w6
Rancher cloud credentials can be used through proxy API by users without access
Critical Also affects github.com/rancher/rancher
GHSA-hwm2-4ph6-w6m5
Rancher's restricted PodSecurityPolicy does not prevent containers from running as a privileged user
High Also affects github.com/rancher/rancher
GHSA-mc24-7m59-4q5p
Rancher CLI skips TLS verification on Rancher CLI login command
Medium Also affects github.com/rancher/rancher
GHSA-mw39-9qc2-f7mg
Rancher exposes sensitive information through audit logs
Medium Also affects github.com/rancher/rancher
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