CVE-2026-26963 in Cilium
Summary
by MITRE • 02/20/2026
Cilium is a networking, observability, and security solution with an eBPF-based dataplane. Versions 1.18.0 through 1.18.5 will incorrectly permit traffic from Pods on other nodes when Native Routing, WireGuard and Node Encryption are enabled. This issue has been fixed in version 1.18.6.
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Analysis
by VulDB Data Team • 02/23/2026
The vulnerability identified as CVE-2026-26963 affects Cilium, a widely adopted networking, observability, and security solution that leverages eBPF-based dataplane technologies for network policy enforcement and traffic management. This security flaw exists within Cilium versions 1.18.0 through 1.18.5 and specifically impacts deployments utilizing Native Routing, WireGuard, and Node Encryption configurations. The issue represents a significant deviation from expected network security boundaries where pod-to-pod communication should be properly isolated based on node membership and network policies.
The technical flaw manifests as an incorrect access control mechanism that fails to properly enforce network isolation when multiple networking components are simultaneously enabled. When Native Routing, WireGuard encryption, and Node Encryption are configured together, Cilium's dataplane fails to maintain proper boundary enforcement between pods running on different nodes within the same cluster. This misconfiguration allows pods on one node to communicate with pods on other nodes without proper authorization, effectively bypassing the intended network segmentation that should exist between nodes in a Kubernetes environment.
From an operational impact perspective, this vulnerability creates a serious security risk for containerized environments that rely on Cilium for network policy enforcement. The flaw essentially enables lateral movement attacks where malicious actors could potentially access workloads running on different nodes within the same cluster, undermining the fundamental security principle of node isolation. This issue particularly affects multi-tenant environments or scenarios where network segmentation between different node groups is critical for compliance and security requirements. The vulnerability exists in the eBPF dataplane implementation and affects traffic flow at the kernel level, making it particularly challenging to detect and remediate without proper monitoring and network analysis capabilities.
The fix implemented in Cilium version 1.18.6 addresses the core issue by correcting the network policy enforcement logic within the eBPF-based dataplane when Native Routing, WireGuard, and Node Encryption are simultaneously enabled. This patch ensures proper boundary enforcement between nodes and restores the expected isolation properties that should prevent unauthorized cross-node communication. Organizations should prioritize upgrading to version 1.18.6 or later to mitigate this vulnerability, while also implementing proper network monitoring to detect any potential exploitation attempts. This vulnerability aligns with CWE-284 (Improper Access Control) and could potentially be leveraged by attackers following ATT&CK techniques related to privilege escalation and lateral movement within containerized environments.
The security implications of this vulnerability extend beyond simple network access control as it fundamentally undermines the security posture of Kubernetes clusters relying on Cilium for network policy enforcement. Organizations should conduct immediate vulnerability assessments to identify affected deployments and implement proper network segmentation monitoring to detect unauthorized traffic patterns. The issue demonstrates the complexity of modern container networking solutions and the critical importance of proper testing and validation when combining multiple security features within a single networking stack.