The vulnerability identified as CVE-2021-25736 concerns the kube-proxy component within Kubernetes on Windows. This vulnerability allows kube-proxy to unintentionally forward network traffic to local processes that are listening on the same port as a LoadBalancer Service. This occurs when the LoadBalancer controller fails to set the 'status.loadBalancer.ingress[].ip' field. Systems where this field is appropriately set by the LoadBalancer controller are not affected by this issue.
The severity of this vulnerability is classified as medium, with a CVSS score of 5.8. This indicates a moderate level of risk, particularly as it involves network exposure with high attack complexity and necessitates high privileges for exploitation. Consequently, organizations should prioritize patching immediately to mitigate the associated risks.
Current exploitation status reveals that there is no known public exploit for this vulnerability, and it is not currently actively exploited in the wild. However, organizations must remain vigilant and address this vulnerability promptly.
To maintain operational security and avoid potential abuse, it is crucial for organizations leveraging Kubernetes on Windows to assess their configurations and apply necessary updates as soon as possible.
Vulnerability Details
The official description states that kube-proxy on Windows can unintentionally forward traffic to local processes listening on the same port as a LoadBalancer Service when the LoadBalancer controller does not set the 'status.loadBalancer.ingress[].ip' field. Clusters where this field is set are unaffected.
This vulnerability is classified under CWE-114, which indicates improper access control. The CVSS score of 5.8 signifies a medium severity level, with high confidentiality impact but no integrity or availability impact.
Technical Analysis
The root cause of the vulnerability lies in the kube-proxy configuration on Windows, which does not adequately segregate traffic intended for LoadBalancer Services from local processes. The attack vector is network-based, with high attack complexity due to the requirement for high privileges to exploit this vulnerability.
To exploit this vulnerability, an attacker would need high privileges and could potentially intercept sensitive traffic. User interaction is not required, but the impacts on confidentiality are significant.
Risk & Impact Analysis
Risk to organizations includes the potential leakage of sensitive data if an attacker successfully exploits this vulnerability. Given its complexity and the requirement for high privileges, the immediate risk may vary based on the specific deployment and operational context.
Organizations using Kubernetes in sensitive environments should assess the potential blast radius of this vulnerability, particularly in multi-tenant configurations where local processes might be exposed.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The affected versions include Kubernetes versions 1.18.0 to 1.18.17, 1.19.0 to 1.19.9, and 1.20.0 to 1.20.5. Organizations are advised to update to the latest versions to mitigate this vulnerability.
Mitigation & Remediation
Organizations should prioritize patching Kubernetes to the latest version to mitigate the risk associated with this vulnerability. Recommended actions include reviewing the LoadBalancer controller configuration to ensure the 'status.loadBalancer.ingress[].ip' field is set correctly.
For organizations unable to immediately patch, consider implementing network segmentation to limit exposure to potentially vulnerable services. Additionally, monitoring network traffic for unusual patterns can aid in early detection of any attempts to exploit this vulnerability.
For further guidance on secure configurations, organizations may refer to the application security assessment resources.
Detection Guidance
To detect potential exploitation attempts, organizations should monitor logs for any abnormal traffic patterns, particularly to and from LoadBalancer Services. Additionally, observe for changes in local processes that may indicate unauthorized access.
Implementing network intrusion detection systems (NIDS) can assist in identifying suspicious activities related to this vulnerability.
AppSecure Threat Intelligence Insight
The long-term significance of CVE-2021-25736 lies in its potential to expose sensitive data and local resources to unauthorized access. This vulnerability highlights the importance of proper configuration within Kubernetes deployments, particularly in cloud environments where misconfigurations can lead to significant security breaches.
Security teams should leverage this incident to strengthen their configuration management practices and ensure rigorous testing of network policies. The vulnerability also serves as a reminder to continuously monitor Kubernetes environments for compliance with best practices.
For more insights on enhancing security measures, organizations can explore the following resources: penetration testing methodology, vulnerability management program design, and cloud penetration testing guide to support their security initiatives.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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