GHSA-g42g-737j-qx6j CVE-2021-25735 GO-2022-0907
Access Restriction Bypass in kube-apiserver
- Severity
- 6.5 / 10
- Medium · CVSS 3.1
- Exploit chance (EPSS)
- 5.38%
- Chance of exploitation in the next 30 days. Higher than 92.66% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-284 Improper Access Control
- CWE-372 Incomplete Internal State Distinction
- CWE-863 Incorrect Authorization
- Fix
1.20.6- Upgrade k8s.io/kubernetes to this version or later
Description
A vulnerability in Kubernetes kube-apiserver could allow node updates to bypass a Validating Admission Webhook and allow unauthorized node updates. The information that is provided to the admission controller could contain old configurations that overwrite values used for validation. Since the overwriting takes place before the validation, this could lead the admission controller to accept requests that should be blocked. The vulnerability can be exploited when an update action on node resources is performed and an admission controller is in place and configured to validate the action.
Users are only affected by this vulnerability if they are running a Validating Admission Webhook for Nodes that denies admission based partially on the old state of the Node object. It only impacts validating admission plugins that rely on old values in certain fields and does not impact calls from kubelets that go through the built-in NodeRestriction admission plugin.
Affected versions
Go
| Package | Vulnerable | Fixed in |
|---|---|---|
| k8s.io/kubernetes | >= 1.20.0, < 1.20.6 |
1.20.6 |
| k8s.io/kubernetes | >= 1.19.0, < 1.19.10 |
1.19.10 |
| k8s.io/kubernetes | < 1.18.18 |
1.18.18 |
| k8s.io/kubernetes | < 1.18.18>= 1.19.0, < 1.19.10>= 1.20.0, < 1.20.6 |
1.18.181.19.101.20.6 |
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.
k8s.io/kubernetes Go → 1.20.6
- go
go get k8s.io/kubernetes@v1.20.6 && go mod tidy
Severity breakdown
CVSS 3.1 6.5
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- High
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- High
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-372: Incomplete Internal State Distinction
The product does not properly determine which state it is in, causing it to assume it is in state X when in fact it is in state Y, causing it to perform incorrect operations in a security-relevant manner.
CWE-863: Incorrect Authorization
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
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
- github.com/kubernetes/kubernetes/issues/100096
- github.com/kubernetes/kubernetes/pull/99946
- github.com/kubernetes/kubernetes/commit/00e81db174ef7aca497be5f42d87e46d14df2a90
- bugzilla.redhat.com/show_bug.cgi
- groups.google.com/g/kubernetes-security-announce/c/FKAGqT4jx9Y
- pkg.go.dev/k8s.io/kubernetes@v1.23.5/cmd/kube-apiserver
- sysdig.com/blog/cve-2021-25735-kubernetes-admission-bypass
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-r6j8-c6r2-37rr kube-controller-manager is vulnerable to half-blind Server Side Request Forgery through in-tree Portworx StorageClass | Medium | Also affects k8s.io/kubernetes |
| GHSA-4x4m-3c2p-qppc Kubernetes Nodes can delete themselves by adding an OwnerReference | Medium | Also affects k8s.io/kubernetes |
| GHSA-hj2p-8wj8-pfq4 kubernetes allows nodes to bypass dynamic resource allocation authorization checks | Low | Also affects k8s.io/kubernetes |
| GO-2025-3547 Kubernetes kube-apiserver Vulnerable to Race Condition | Low | Also affects k8s.io/kubernetes |
| GHSA-3wgm-2gw2-vh5m Kubernetes GitRepo Volume Inadvertent Local Repository Access | Medium | Also affects k8s.io/kubernetes |
| GHSA-vv39-3w5q-974q Kubernetes allows Command Injection affecting Windows nodes via nodes/*/logs/query API | Medium | Also affects k8s.io/kubernetes |
| GHSA-jgfp-53c3-624w Node Denial of Service via kubelet Checkpoint API | Medium | Also affects k8s.io/kubernetes |
| GHSA-27wf-5967-98gx Kubernetes kubelet arbitrary command execution | High | Also affects k8s.io/kubernetes |
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