Summary
A certificate validation flaw in maclof kubernetes-client can disable TLS server certificate verification when kubeconfig data lacks certificate-authority-data. An on-path attacker may impersonate the Kubernetes API server, capture authentication credentials, or alter REST and WebSocket traffic.
A certificate validation flaw in maclof kubernetes-client can disable TLS server certificate verification when kubeconfig data lacks certificate-authority-data. An on-path attacker may impersonate the Kubernetes API server, capture authentication credentials, or alter REST and WebSocket traffic.
Affected context
The issue occurs in deployments using affected kubernetes-client releases where kubeconfig files are processed through parseKubeconfig() or parseKubeconfigFile(). Risk is higher when a kubeconfig omits certificate-authority-data and the client relies on the resulting TLS configuration without independently confirming that certificate verification remains enabled.
The issue occurs in deployments using affected kubernetes-client releases where kubeconfig files are processed through parseKubeconfig() or parseKubeconfigFile(). Risk is higher when a kubeconfig omits certificate-authority-data and the client relies on the resulting TLS configuration without independently confirming that certificate verification remains enabled.
Exploit preconditions
- Attack surface: TLS connections from the Kubernetes client to the API server
- Required access: Network positioning that permits interception or redirection of client traffic
- Trigger point: Parsing and applying a kubeconfig that lacks certificate-authority-data
- Why exploitation is possible: The client can proceed without validating the API server certificate and may not correctly honor the kubeconfig's
insecure-skip-tls-verifysetting
- Attack surface: TLS connections from the Kubernetes client to the API server
- Required access: Network positioning that permits interception or redirection of client traffic
- Trigger point: Parsing and applying a kubeconfig that lacks certificate-authority-data
- Why exploitation is possible: The client can proceed without validating the API server certificate and may not correctly honor the kubeconfig's
insecure-skip-tls-verifysetting
Why this happens
The underlying bug is improper certificate validation, mapped to CWE-295. Kubeconfig parsing establishes TLS behavior based on the presence or absence of certificate authority data, but the implementation can treat missing trust material as a reason to disable verification rather than as an invalid or incomplete security configuration. This creates a trust-boundary failure in which an untrusted endpoint may be accepted as the Kubernetes API server.
The underlying bug is improper certificate validation, mapped to CWE-295. Kubeconfig parsing establishes TLS behavior based on the presence or absence of certificate authority data, but the implementation can treat missing trust material as a reason to disable verification rather than as an invalid or incomplete security configuration. This creates a trust-boundary failure in which an untrusted endpoint may be accepted as the Kubernetes API server.
Potential impact
- An on-path attacker may impersonate the Kubernetes API server
- Bearer tokens or Basic authentication credentials could be captured
- REST API requests may be modified in transit
- WebSocket traffic could be intercepted or tampered with
- Kubernetes resources or cluster operations could be affected through stolen credentials
- An on-path attacker may impersonate the Kubernetes API server
- Bearer tokens or Basic authentication credentials could be captured
- REST API requests may be modified in transit
- WebSocket traffic could be intercepted or tampered with
- Kubernetes resources or cluster operations could be affected through stolen credentials
General mitigation guidance
Mitigation generally focuses on ensuring that TLS certificate verification is enabled by default and cannot be silently disabled because trust configuration is incomplete.
Common defensive patterns include:
- Rejecting kubeconfig files that lack an explicitly defined and trusted certificate authority when verification is required
- Applying strict, consistent handling of
insecure-skip-tls-verifyrather than inferring security behavior from missing fields - Using managed trust stores or pinned, validated certificate authorities
- Protecting kubeconfig files and credentials from unauthorized modification or disclosure
- Limiting the privileges and scope of Kubernetes credentials used by clients
- Monitoring network paths and enforcing secure transport policies between clients and API servers
Mitigation generally focuses on ensuring that TLS certificate verification is enabled by default and cannot be silently disabled because trust configuration is incomplete.
Common defensive patterns include:
- Rejecting kubeconfig files that lack an explicitly defined and trusted certificate authority when verification is required
- Applying strict, consistent handling of
insecure-skip-tls-verifyrather than inferring security behavior from missing fields - Using managed trust stores or pinned, validated certificate authorities
- Protecting kubeconfig files and credentials from unauthorized modification or disclosure
- Limiting the privileges and scope of Kubernetes credentials used by clients
- Monitoring network paths and enforcing secure transport policies between clients and API servers
How teams detect issues like this
Organizations can look for:
- Static analysis rules covering TLS clients that disable verification when CA material is absent
- Code review signals such as permissive defaults, conditional omission of certificate verification, or ignored security-related configuration fields
- Tests that exercise kubeconfigs with missing, malformed, and conflicting TLS settings
- Policy checks requiring explicit certificate verification for Kubernetes API connections
- Network monitoring for unexpected API-server certificates, endpoints, or downgraded trust behavior
Automated security review tools may help identify insecure TLS configuration and inconsistent kubeconfig parsing.
Organizations can look for:
- Static analysis rules covering TLS clients that disable verification when CA material is absent
- Code review signals such as permissive defaults, conditional omission of certificate verification, or ignored security-related configuration fields
- Tests that exercise kubeconfigs with missing, malformed, and conflicting TLS settings
- Policy checks requiring explicit certificate verification for Kubernetes API connections
- Network monitoring for unexpected API-server certificates, endpoints, or downgraded trust behavior
Automated security review tools may help identify insecure TLS configuration and inconsistent kubeconfig parsing.
