CVE-2019-9946 in CNI
Summary
by MITRE
Cloud Native Computing Foundation (CNCF) CNI (Container Networking Interface) 0.7.4 has a network firewall misconfiguration which affects Kubernetes. The CNI 'portmap' plugin, used to setup HostPorts for CNI, inserts rules at the front of the iptables nat chains; which take precedence over the KUBE- SERVICES chain. Because of this, the HostPort/portmap rule could match incoming traffic even if there were better fitting, more specific service definition rules like NodePorts later in the chain. The issue is fixed in CNI 0.7.5 and Kubernetes 1.11.9, 1.12.7, 1.13.5, and 1.14.0.
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Analysis
by VulDB Data Team • 08/21/2023
The vulnerability described in CVE-2019-9946 represents a critical network firewall misconfiguration within the Container Networking Interface (CNI) implementation used by Kubernetes environments. This flaw specifically impacts the 'portmap' plugin version 0.7.4, which is responsible for setting up HostPorts in containerized environments. The issue arises from improper iptables rule ordering where the portmap plugin inserts its rules at the beginning of the iptables nat chains, creating a precedence problem that undermines the intended network security architecture. This misconfiguration directly affects Kubernetes clusters that rely on CNI for network management, potentially exposing services to unintended traffic routing and access control violations.
The technical root cause of this vulnerability stems from the improper placement of iptables rules within the network filtering chain structure. When the portmap plugin inserts its rules at the front of the iptables nat chains, these rules take precedence over the KUBE-SERVICES chain that contains more specific service definitions including NodePorts. This rule ordering issue creates a situation where incoming traffic destined for legitimate Kubernetes services may be intercepted by the portmap rules before reaching the proper service routing mechanisms. The vulnerability manifests as a privilege escalation vector where unauthorized network access can occur through improperly ordered firewall rules, effectively bypassing the intended service discovery and load balancing mechanisms that Kubernetes relies upon for secure service exposure.
From an operational impact perspective, this vulnerability exposes Kubernetes clusters to significant security risks including potential unauthorized access to containerized applications and services. The misconfiguration allows for traffic that should be properly routed through Kubernetes service definitions to instead be handled by the portmap plugin's rules, potentially creating attack vectors for lateral movement within the cluster. This issue particularly affects clusters using HostPort configurations, where applications require direct mapping of host network ports to container ports, making it a critical concern for environments that expose services directly to external networks. The vulnerability also impacts the integrity of Kubernetes network policies and service routing mechanisms, potentially allowing attackers to bypass security controls designed to protect cluster resources.
The mitigation strategy for CVE-2019-9946 requires immediate upgrading to CNI version 0.7.5 or later, alongside corresponding Kubernetes version updates including 1.11.9, 1.12.7, 1.13.5, and 1.14.0. Organizations should also implement immediate network monitoring to detect any anomalies in traffic routing patterns that might indicate exploitation attempts. Security teams should conduct comprehensive audits of their iptables configurations to identify and correct any improper rule ordering that might exist in their environments. This vulnerability aligns with CWE-284 Access Control Issues and maps to ATT&CK technique T1068, which involves exploiting weaknesses in privilege and access control mechanisms. The fix implemented in the updated versions addresses the fundamental rule ordering problem by ensuring proper sequence of iptables rules, thereby restoring the intended security posture and service routing behavior within Kubernetes clusters. Organizations should also consider implementing network segmentation strategies and additional monitoring controls to detect similar issues in other network components that might exhibit similar rule ordering vulnerabilities.