CVE-2019-11243 in Kubernetes
Summary
by MITRE
In Kubernetes v1.12.0-v1.12.4 and v1.13.0, the rest.AnonymousClientConfig() method returns a copy of the provided config, with credentials removed (bearer token, username/password, and client certificate/key data). In the affected versions, rest.AnonymousClientConfig() did not effectively clear service account credentials loaded using rest.InClusterConfig()
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 09/06/2023
The vulnerability identified as CVE-2019-11243 affects Kubernetes versions 1.12.0 through 1.12.4 and 1.13.0, representing a critical security flaw in the Kubernetes API client configuration handling mechanism. This issue resides within the rest package of the Kubernetes client-go library, specifically impacting how anonymous client configurations are generated and processed. The vulnerability stems from a design flaw in the AnonymousClientConfig() method which is intended to strip authentication credentials from API client configurations to enable anonymous access to Kubernetes resources. The flaw manifests when the method fails to properly remove service account credentials that have been loaded using the rest.InClusterConfig() function, creating a potential security risk where sensitive authentication data might persist in configurations intended to be anonymous.
The technical implementation of this vulnerability involves the improper handling of credential stripping within the Kubernetes client-go library's configuration management system. When rest.AnonymousClientConfig() is invoked, it should create a clean configuration copy devoid of any authentication tokens, username/password combinations, or client certificate information. However, the affected versions contain a logic error where service account credentials loaded through rest.InClusterConfig() are not effectively cleared from the configuration object. This occurs because the method does not properly account for service account tokens that are automatically loaded when running within a Kubernetes cluster environment, leading to a scenario where authentication data persists in configurations that should be anonymous. The flaw essentially creates a credential leakage vector where sensitive service account information remains accessible through configuration objects that are meant to be stripped of all authentication details.
The operational impact of this vulnerability extends beyond simple credential exposure, potentially enabling unauthorized access to Kubernetes cluster resources and compromising cluster security. An attacker who can manipulate or access configurations that should be anonymous could potentially leverage the retained service account credentials to gain elevated privileges within the cluster. This vulnerability affects Kubernetes clusters that utilize service accounts for authentication and authorization, particularly those where applications or components might generate anonymous client configurations for API access. The risk is amplified in environments where multiple components or services interact with the Kubernetes API, as the persistence of service account credentials could allow attackers to maintain access even when other authentication mechanisms are disabled or compromised. This flaw directly impacts the principle of least privilege and could enable privilege escalation attacks against cluster resources.
Mitigation strategies for CVE-2019-11243 focus on both immediate remediation and long-term architectural improvements. The primary solution involves upgrading to Kubernetes versions 1.12.5 or 1.13.1, where the vulnerability has been patched to properly clear all authentication credentials including service account tokens. Organizations should implement comprehensive configuration auditing to identify any components that might be using the vulnerable AnonymousClientConfig() method and ensure all affected applications are updated. Security teams should also conduct thorough reviews of service account usage patterns and implement proper credential rotation policies. The vulnerability aligns with CWE-284 Access Control Issues and can be categorized under ATT&CK technique T1078 Valid Accounts, as it involves improper handling of authentication credentials that could lead to unauthorized access. Organizations should also consider implementing runtime monitoring to detect anomalous API access patterns that might indicate credential leakage from vulnerable configurations. Proper security configuration management and regular vulnerability assessments are essential to prevent exploitation of this class of credential handling flaws in container orchestration environments.