CVE-2026-86831 Overview
CVE-2026-86831 is a NetworkPolicy enforcement bypass in the Amazon EKS Network Policy Agent (aws-network-policy-agent) prior to version 1.4.0. The agent fails to properly validate the uniqueness of pod identifiers, allowing crafted pod and namespace names to produce identifier collisions. An authenticated remote user can exploit this collision to bypass Kubernetes NetworkPolicy enforcement on co-located pods residing in other namespaces. The flaw is tracked under CWE-1289: Improper Validation of Specified Input to API. Remediation requires upgrading to Amazon EKS Network Policy Agent 1.4.0 or later, or Amazon VPC CNI Managed Add-on v1.22.4 or later, which bundles the fixed agent.
Critical Impact
Authenticated tenants can bypass namespace-scoped NetworkPolicy enforcement and reach isolated workloads on the same node, undermining a core Kubernetes multi-tenancy control.
Affected Products
- Amazon EKS Network Policy Agent versions prior to 1.4.0
- Amazon VPC CNI Managed Add-on versions prior to v1.22.4
- Amazon EKS clusters relying on the affected agent for NetworkPolicy enforcement
Discovery Timeline
- 2026-09-16 - CVE-2026-86831 published to NVD
- 2026-09-16 - Last updated in NVD database
Technical Details for CVE-2026-86831
Vulnerability Analysis
The aws-network-policy-agent translates Kubernetes NetworkPolicy resources into enforcement rules applied to pods running on EKS worker nodes. To identify a pod within its data plane, the agent computes a pod identifier that is expected to be unique across the cluster. The vulnerability arises because this identifier derivation does not adequately isolate the pod name from the namespace name. Attackers who can create workloads in a namespace can supply pod and namespace name combinations that collide with legitimate pods elsewhere in the cluster. When a collision occurs, the enforcement engine associates one pod's policy state with a foreign pod, producing incorrect allow decisions.
Root Cause
The root cause is improper validation of specified input to an API, tracked as CWE-1289. The agent constructs pod identifiers from user-controlled name fields without enforcing a canonical, non-ambiguous encoding. Two distinct pods in different namespaces can therefore map to the same internal identifier used for policy lookup.
Attack Vector
An authenticated user with permission to create pods and namespaces in an EKS cluster crafts resource names designed to collide with a target pod's identifier. Once the malicious pod is scheduled onto the same node as the target, the agent's collision causes NetworkPolicy rules to be misapplied. Traffic that policy would otherwise deny is permitted between namespaces, enabling lateral movement across tenant boundaries. Exploitation does not require code execution on the node or elevated Kubernetes RBAC beyond standard namespace-scoped workload creation privileges granted to tenants.
No public proof-of-concept exploit code has been released. Refer to the GitHub Security Advisory GHSA-7xv7-8r3j-3j25 for vendor-supplied technical details.
Detection Methods for CVE-2026-86831
Indicators of Compromise
- Pod or namespace names containing unusual delimiter characters, embedded slashes, or padded strings that appear engineered to mimic another workload's identifier.
- Pods scheduled by low-privilege service accounts that share a node with sensitive workloads in unrelated namespaces.
- Unexpected cross-namespace traffic recorded in VPC flow logs or CNI datapath logs that should have been denied by an active NetworkPolicy.
Detection Strategies
- Audit Kubernetes API server logs for create requests on pods and namespaces with names that contain suspicious character patterns or excessive length.
- Compare NetworkPolicy intent against observed east-west traffic using CNI flow logs to identify enforcement anomalies.
- Inventory nodes running amazon-vpc-cni-k8s versions below v1.22.4 and aws-network-policy-agent below 1.4.0.
Monitoring Recommendations
- Enable and centralize EKS control plane audit logs and VPC CNI Network Policy logs for correlation.
- Alert on new pods created in tenant namespaces that co-locate with pods in privileged namespaces such as kube-system.
- Track add-on versions across managed node groups and Fargate profiles to confirm patch coverage.
How to Mitigate CVE-2026-86831
Immediate Actions Required
- Upgrade aws-network-policy-agent to version 1.4.0 or later on all EKS clusters.
- Upgrade the Amazon VPC CNI Managed Add-on to v1.22.4 or later, which includes the fixed agent.
- Review NetworkPolicy resources and validate that expected deny rules are enforced after the upgrade.
Patch Information
AWS published fixed releases in aws-network-policy-agent v1.4.0 and amazon-vpc-cni-k8s v1.22.4. Additional guidance is available in the AWS Security Bulletin 2026-113 and the coordinated advisories GHSA-gjc7-c7mx-x8f3 and GHSA-7xv7-8r3j-3j25.
Workarounds
- Restrict create and update permissions on namespaces and pods to trusted administrators to reduce the population of users who can craft colliding identifiers.
- Apply Kubernetes admission controls, such as OPA Gatekeeper or Kyverno, to constrain acceptable pod and namespace naming patterns.
- Where feasible, use node isolation or dedicated node groups to prevent untrusted tenant workloads from co-locating with sensitive pods.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
