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Rancher's restricted PodSecurityPolicy does not prevent containers from running as a privileged user

High severity GitHub Reviewed Published Mar 31, 2022 in rancher/rancher

Package

gomod github.com/rancher/rancher (Go)

Affected versions

>= 2.0.0, < 2.6.4

Patched versions

2.6.4

Description

Impact

The restricted pod security policy (PSP), provided in Rancher versions from 2.0 up to and including 2.6.3, has a deviation from the upstream restricted policy provided in Kubernetes, in which Rancher's PSP has runAsUser set to runAsAny, while upstream has runAsUser set to MustRunAsNonRoot. This allows containers to run as any user, including a privileged user (root), even when Rancher's restricted policy is enforced on a project or at cluster level.

A new restricted-noroot PSP was created to prevent pods from running as root when this policy is enforced. This new policy was introduced, instead of patching the current provided restricted policy, in order to avoid breaking users' workloads that are using the restricted PSP and that might be running as a privileged user.

Note: Running containers as root increases the risk of a compromised container being used by a malicious actor as an attack platform to further exploit the user's environment. It is a security best practice to avoid running containers as a privileged user and to limit its usage to workloads where it is strictly necessary.

Patches

Patched versions include release 2.6.4 and later versions. The existing restricted PSP in Rancher 2.6.4 was not modified and still allows containers to run as a privileged user, as explained above. This fix was not backported to previous releases.

For Rancher 2.6.4 and later releases, users using the current restricted PSP and that want to prevent containers from running as root, are advised to migrate to the new restricted-noroot policy. Before doing this migration, it is necessary to verify if affected workloads are currently running as a privileged user and modify them accordingly to the users' own environment to run as a non-privileged user. A redeployment of the affected workload is necessary in order for the new PSP to take effect.

Workarounds

For users running Rancher 2.6.3 and previous releases, which did not received this backport and that want to benefit from this fix, they can manually create a new restricted-noroot PSP on their clusters through Rancher UI. The template of the restricted-noroot policy provided in Rancher 2.6.4 is available in the source code. As a reminder, it is also necessary to manually verify and redeploy the running workload before enabling a more restricted pod security policy.

References

For instructions on how to configure pod security policies using Rancher, please refer to the documentation page. For more information on PSPs in Kubernetes, please refer to the Kubernetes documentation (permalink).

Important reminder: Pod security policies are considered deprecated since Kubernetes v1.21, and will be removed in Kubernetes v1.25. Consult Kubernetes' documentation (permalink) regarding how to migrate from PodSecurityPolicy to Kubernetes' built-in PodSecurity Admission Controller. For the list of supported Kubernetes versions in Rancher, please consult our support matrix.

For more information

If you have any questions or comments about this advisory:

References

@macedogm macedogm published to rancher/rancher Mar 31, 2022
Published to the GitHub Advisory Database Mar 3, 2026
Reviewed Mar 3, 2026

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 v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required Low
User interaction None
Vulnerable System Impact Metrics
Confidentiality None
Integrity High
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

EPSS score

Weaknesses

Missing Authorization

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

CVE ID

No known CVE

GHSA ID

GHSA-hwm2-4ph6-w6m5

Source code

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