Detecting and Mitigating CVE-2021-25737: EndpointSlice validation enables host network hijack

CVE-2021-25737 is a low-severity vulnerability in Kubernetes' kube-apiserver that allows an authorized user to hijack network traffic by redirecting pod traffic to private networks through EndpointSlices, potentially leading to sensitive data leaks. This issue affects specific versions of Kubernetes, including v1.16.0 to v1.21. The vulnerability is due to the lack of validation preventing modifications of EndpointSlices to include addresses in the 127.0.0.0/8 and 169.254.0.0/16 ranges. Mitigation involves upgrading kube-apiserver to patched versions or implementing a validating admission webhook to prevent the creation and modification of EndpointSlices with such addresses. Detection of exploitation attempts can be achieved using the open-source tool Falco by enabling Kubernetes Audit Logging to monitor suspicious activities. The article emphasizes the importance of adhering to container security best practices and the role of tools like Sysdig Secure and Falco in safeguarding Kubernetes environments.