CVE-2026-6437: AWS EFS CSI Driver Auth Bypass Vulnerability

CVE-2026-6437 Overview

CVE-2026-6437 is a command injection vulnerability affecting the AWS EFS CSI Driver (aws-efs-csi-driver) prior to version v3.0.1. The vulnerability exists in the volume handling component, where improper neutralization of argument delimiters allows remote authenticated users with PersistentVolume creation permissions to inject arbitrary mount options via comma injection.

This vulnerability is classified as CWE-88 (Improper Neutralization of Argument Delimiters in a Command), a weakness that occurs when user input is improperly sanitized before being used in command construction, allowing attackers to manipulate command arguments.

Critical Impact

Attackers with PersistentVolume creation permissions can inject arbitrary mount options, potentially compromising container integrity and accessing sensitive data across Kubernetes clusters running AWS EFS workloads.

Affected Products

• AWS EFS CSI Driver (aws-efs-csi-driver) versions prior to v3.0.1
• Kubernetes clusters using vulnerable EFS CSI driver versions
• AWS EKS environments with EFS storage integration

Discovery Timeline

• April 17, 2026 - CVE-2026-6437 published to NVD
• April 20, 2026 - Last updated in NVD database

Technical Details for CVE-2026-6437

Vulnerability Analysis

The vulnerability resides in how the AWS EFS CSI Driver processes mount options during PersistentVolume creation. The driver fails to properly sanitize user-controlled input, specifically comma-separated values that are used to construct mount command arguments. This improper neutralization allows authenticated attackers to break out of the intended parameter context and inject additional mount options.

In Kubernetes environments, the Container Storage Interface (CSI) driver handles the mounting of EFS file systems to pods. When a PersistentVolume is created with attacker-controlled mount options, the vulnerable code path does not escape or validate comma characters, which serve as argument delimiters in the mount command construction.

The vulnerability requires the attacker to have permissions to create PersistentVolume resources, which is typically restricted to cluster administrators or users with elevated RBAC permissions. However, in multi-tenant Kubernetes environments or misconfigured clusters, this permission boundary may be weaker than intended.

Root Cause

The root cause is insufficient input validation in the volume handling component of the AWS EFS CSI Driver. The driver constructs mount commands by concatenating user-supplied mount options without properly escaping or validating delimiter characters. This allows comma injection attacks where an attacker can terminate the current argument and introduce additional mount options that were not intended by administrators.

Attack Vector

The attack requires network access and authenticated access to the Kubernetes API with PersistentVolume creation permissions. An attacker crafts a malicious PersistentVolume manifest containing specially crafted mount options with embedded comma characters. When the CSI driver processes this volume and attempts to mount the EFS file system, the injected mount options are interpreted as separate arguments, potentially allowing the attacker to specify arbitrary mount configurations.

The attack flow involves:

1. Attacker creates a PersistentVolume with malicious mountOptions containing comma-injected values
2. The EFS CSI driver processes the volume creation request
3. Malicious mount options are passed to the underlying mount command without proper sanitization
4. Injected mount options take effect, potentially enabling access to unauthorized resources or modifying mount behavior

Since no verified code examples are available, readers should refer to the GitHub Security Advisory GHSA-mph4-q2vm-w2pw for detailed technical information about the vulnerability mechanism and exploitation techniques.

Detection Methods for CVE-2026-6437

Indicators of Compromise

• Unusual PersistentVolume resources with suspicious mountOptions containing multiple comma characters
• EFS CSI driver pod logs showing unexpected mount option combinations
• Failed mount operations followed by successful mounts with modified parameters
• Kubernetes audit logs showing PersistentVolume creation with malformed specifications

Detection Strategies

• Implement Kubernetes admission controllers to validate PersistentVolume mount options before creation
• Monitor Kubernetes audit logs for PersistentVolume creation events, particularly those with complex mount option strings
• Review EFS CSI driver logs for anomalous mount command constructions
• Use SentinelOne Singularity Cloud Security to detect suspicious container and Kubernetes activity patterns

Monitoring Recommendations

• Enable detailed audit logging for PersistentVolume and PersistentVolumeClaim resources
• Configure alerts for PersistentVolume creation by non-administrative users
• Monitor EFS mount activity for unexpected mount option configurations
• Implement runtime security monitoring for CSI driver containers

How to Mitigate CVE-2026-6437

Immediate Actions Required

• Upgrade AWS EFS CSI Driver to version v3.0.1 or later immediately
• Review existing PersistentVolume resources for suspicious mount options
• Audit RBAC permissions to ensure PersistentVolume creation is restricted to authorized users
• Implement admission controllers to validate mount options on PersistentVolume creation

Patch Information

AWS has released version v3.0.1 of the EFS CSI Driver which addresses this vulnerability. The patch properly sanitizes comma characters and other argument delimiters in user-supplied mount options before constructing mount commands.

For detailed patch information, refer to the GitHub Release v3.0.1 and the AWS Security Bulletin 2026-016.

Workarounds

• Restrict PersistentVolume creation permissions using Kubernetes RBAC to trusted administrators only
• Implement OPA Gatekeeper or Kyverno policies to validate and sanitize mount options in PersistentVolume specs
• Use network policies to limit which pods can communicate with the EFS CSI driver
• Consider temporarily disabling dynamic EFS provisioning until the patch can be applied

# Upgrade EFS CSI Driver via Helm
helm repo update
helm upgrade aws-efs-csi-driver aws-efs-csi-driver/aws-efs-csi-driver \
  --namespace kube-system \
  --set image.tag=v3.0.1

# Verify the upgrade
kubectl get pods -n kube-system -l app=efs-csi-controller -o jsonpath='{.items[*].spec.containers[*].image}'