CVE-2026-71208 in KubeSphere
Summary
by MITRE • 08/05/2026
KubeSphere's cluster-controller reconciliation (pkg/utils/clusterclient/clusterclient.go, addCluster) processes every Cluster custom resource's connection configuration and immediately calls Discovery().ServerVersion() against the CRD-specified Kubernetes API endpoint, which is parsed only for URL syntax (url.Parse) with no allow/deny-list for loopback, RFC1918 private ranges, link-local, or cloud-metadata addresses (e.g. 169.254.169.254). A user able to create or update a Cluster CRD can force the controller-manager and apiserver pods to issue outbound requests to arbitrary internal or metadata endpoints.
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Analysis
by VulDB Data Team • 08/05/2026
This vulnerability exists within KubeSphere's cluster-controller component where the reconciliation process handles Cluster custom resources by immediately attempting to establish connections to specified Kubernetes API endpoints. The flaw occurs in the addCluster function located in pkg/utils/clusterclient/clusterclient.go which processes connection configurations without proper validation of the target endpoint addresses. The system relies solely on url.Parse for URL syntax validation while completely omitting checks against established security boundaries including loopback addresses, private RFC1918 ranges such as 10.x.x.x, 172.16.x.x through 172.31.x.x, and 192.168.x.x networks, as well as link-local addresses and cloud metadata endpoints like 169.254.169.254. This oversight creates a significant attack surface where malicious actors can exploit the system to force outbound connections to internal network resources or sensitive metadata services.
The technical implementation of this vulnerability stems from inadequate input validation in the cluster connection handling logic. When users create or update Cluster CRDs, they can specify arbitrary API endpoint URLs that bypass any restrictions on internal address ranges or privileged endpoints. The discovery process immediately attempts to connect to these specified endpoints without first filtering against known dangerous address patterns. This design flaw aligns with CWE-20 Improper Input Validation and represents a classic example of insufficient address validation in network communication components. The vulnerability enables attackers to potentially access internal services, metadata endpoints, or other sensitive resources that should normally be restricted from external access.
The operational impact of this vulnerability is substantial as it allows for both information disclosure and potential lateral movement within the target environment. An attacker with permissions to create or modify Cluster CRDs can force the controller-manager pods to initiate connections to internal systems, potentially exposing sensitive information through metadata services or gaining access to other internal endpoints that are normally protected by network segmentation. The attack vector is particularly dangerous because it leverages legitimate system functionality to achieve unauthorized access to internal resources, making detection more challenging. This vulnerability could enable attackers to gather information about internal network topology, access cloud instance metadata containing credentials, or potentially reach other services within the same network segment that would otherwise be isolated.
The security implications extend beyond simple information disclosure as this vulnerability can facilitate further attacks within the Kubernetes environment and surrounding infrastructure. The ability to force connections to internal endpoints enables potential exploitation of additional vulnerabilities in services running on those addresses, including credential exposure through metadata services or access to internal APIs that may not have proper authentication mechanisms. From an ATT&CK perspective, this vulnerability maps to T1071.004 Application Layer Protocol DNS and potentially T1082 System Information Discovery, while also enabling techniques related to lateral movement and privilege escalation through information gathering. Organizations should implement immediate mitigations including network segmentation controls, egress filtering, and restrictions on Cluster CRD creation permissions to prevent unauthorized access to internal resources.
Effective mitigation strategies include implementing strict allowlists for cluster endpoint addresses that exclude private ranges, loopback addresses, and metadata endpoints while ensuring that the controller only accepts connections to explicitly trusted external addresses. Network-level controls should be deployed to block outbound connections to RFC1918 ranges, link-local addresses, and cloud metadata services from the controller-manager pods. Additionally, proper RBAC controls should limit which users or roles can create or modify Cluster CRDs, ensuring that only privileged administrators have access to this functionality. The system should also implement proper address validation in the url.Parse process by adding checks for dangerous address patterns before attempting any network connections. Organizations should consider implementing monitoring and alerting on outbound connection attempts to unusual addresses as an additional detection mechanism for potential exploitation of this vulnerability.