CVE-2021-20218
📋 TL;DR
This vulnerability in fabric8 kubernetes-client allows malicious pods/containers to exploit the copy command to extract files outside the intended working directory path. Applications using the vulnerable kubernetes-client library for file operations in Kubernetes environments are affected. The primary risks are file integrity compromise and potential system availability impacts.
💻 Affected Systems
- fabric8 kubernetes-client
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Malicious container could extract sensitive system files, configuration data, or secrets from the host or other containers, leading to complete cluster compromise and data exfiltration.
Likely Case
Attackers with pod execution privileges could read files from other containers or the host filesystem, potentially accessing sensitive application data or credentials.
If Mitigated
With proper pod security policies, network segmentation, and least privilege principles, impact would be limited to the compromised container's namespace.
🎯 Exploit Status
Exploitation requires pod/container execution access. The vulnerability is a path traversal issue in the copy command implementation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: kubernetes-client-4.13.2, kubernetes-client-5.0.2, kubernetes-client-4.11.2, kubernetes-client-4.7.2
Vendor Advisory: https://bugzilla.redhat.com/show_bug.cgi?id=1923405
Restart Required: Yes
Instructions:
1. Identify applications using fabric8 kubernetes-client. 2. Update dependency to patched version (4.13.2, 5.0.2, 4.11.2, or 4.7.2). 3. Rebuild and redeploy applications. 4. Restart affected services.
🔧 Temporary Workarounds
Restrict pod security context
allImplement pod security policies to restrict container capabilities and filesystem access
kubectl apply -f pod-security-policy.yaml
Disable copy command usage
allAvoid using kubernetes-client copy command functionality in vulnerable applications
🧯 If You Can't Patch
- Implement strict pod security policies with readOnlyRootFilesystem: true and minimal capabilities
- Use network policies to isolate vulnerable pods and implement egress filtering
🔍 How to Verify
Check if Vulnerable:
Check application dependencies for fabric8 kubernetes-client versions 4.2.0-4.13.1 or 5.0.0-5.0.1Check Version:
mvn dependency:tree | grep kubernetes-client OR check pom.xml/gradle.build filesVerify Fix Applied:
Verify kubernetes-client version is 4.13.2, 5.0.2, 4.11.2, or 4.7.2 in application dependencies📡 Detection & Monitoring
Log Indicators:
- Unusual file access patterns from containers
- Copy operations attempting paths with '../' sequences
- Container accessing files outside expected directories
Network Indicators:
- Unexpected outbound data transfers from containers to external systems
SIEM Query:
container_logs | where operation contains 'copy' and path contains '../'