CVE-2020-8570: Kubernetes Java Path Traversal Flaw

CVE-2020-8570 Overview

CVE-2020-8570 is a path traversal vulnerability affecting Kubernetes Java client libraries in version 10.0.0 and versions prior to 9.0.1. The vulnerability allows writes to paths outside of the current directory when copying multiple files from a remote pod which sends a maliciously crafted archive. This can potentially overwrite any files on the system of the process executing the client code.

Critical Impact

A remote attacker can leverage a malicious Kubernetes pod to send specially crafted archive files that overwrite arbitrary files on the system running the vulnerable Java client, potentially leading to code execution or system compromise.

Affected Products

• Kubernetes Java Client version 10.0.0
• Kubernetes Java Client versions prior to 9.0.1

Discovery Timeline

• 2021-01-21 - CVE CVE-2020-8570 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-8570

Vulnerability Analysis

This vulnerability falls under CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) and CWE-23 (Relative Path Traversal). The flaw exists in the file copy functionality of the Kubernetes Java client library, specifically when handling archive files received from remote pods.

When users utilize the client library to copy files from a Kubernetes pod, the library processes the incoming archive data. The vulnerability arises because the library fails to properly sanitize file paths within the archive before extracting them. An attacker who controls a malicious pod can craft an archive containing files with relative path components (such as ../) that, when extracted, write files outside the intended destination directory.

The attack requires network access and can be exploited without authentication or user interaction. The impact is significant as it affects both the integrity and availability of the system—attackers can overwrite critical system files or application configurations.

Root Cause

The root cause is insufficient validation of file paths extracted from archive data received from remote Kubernetes pods. The Kubernetes Java client library does not properly canonicalize or validate that extracted file paths remain within the intended destination directory, allowing path traversal sequences to escape the target directory structure.

Attack Vector

The attack is network-based and requires the attacker to control or compromise a Kubernetes pod that the victim's Java client connects to for file copy operations. The attacker creates a maliciously crafted archive containing entries with path traversal sequences (e.g., ../../etc/cron.d/malicious). When the victim's application uses the vulnerable Kubernetes Java client to copy files from this pod, the archive is processed and files are written to unintended locations on the host filesystem.

This attack pattern is commonly known as a "Zip Slip" vulnerability, where archive extraction routines fail to properly validate destination paths. The exploitation does not require authentication to the target system and can occur without any user interaction beyond the normal file copy operation.

Detection Methods for CVE-2020-8570

Indicators of Compromise

• Unexpected file modifications in system directories outside of normal Kubernetes working directories
• Archive extraction operations from Kubernetes pods writing to paths containing ../ sequences
• Unusual file creation events in sensitive directories such as /etc, /usr/bin, or application configuration paths
• Log entries showing file operations with path traversal patterns during pod file copy operations

Detection Strategies

• Monitor file system activity for write operations that occur during Kubernetes client file copy operations to directories outside expected paths
• Implement file integrity monitoring (FIM) on critical system directories to detect unauthorized modifications
• Review application logs for errors or anomalies during archive extraction operations from Kubernetes pods
• Deploy endpoint detection rules that alert on path traversal patterns in file operation arguments

Monitoring Recommendations

• Enable detailed logging for applications using the Kubernetes Java client library
• Implement real-time file system monitoring on systems running Kubernetes client applications
• Configure alerts for any file writes to system-critical directories during Kubernetes operations
• Audit all file copy operations from remote pods for suspicious archive contents

How to Mitigate CVE-2020-8570

Immediate Actions Required

• Upgrade Kubernetes Java client library to version 9.0.1 or later (for the 9.x branch) or version 10.0.1 or later (for the 10.x branch)
• Audit applications using the Kubernetes Java client to identify vulnerable deployments
• Review file copy operations from remote pods and restrict access to trusted pods only
• Implement file system access controls to limit the directories writable by applications using the Kubernetes client

Patch Information

The vulnerability has been addressed by the Kubernetes project. Users should upgrade to patched versions of the Java client library. Detailed information about the fix is available in the GitHub Issue Report and the Kubernetes Security Announcement.

Workarounds

• Restrict pod file copy operations to only trusted and verified pods within the Kubernetes cluster
• Implement network segmentation to limit which pods can communicate with systems running the Java client
• Run applications using the Kubernetes Java client with minimal filesystem permissions using principle of least privilege
• Deploy additional file system access controls that prevent writes to sensitive directories regardless of application permissions

# Verify your Kubernetes Java client version
mvn dependency:tree | grep kubernetes-client

# Upgrade to patched version in Maven pom.xml
# For 9.x branch: upgrade to 9.0.1 or later
# For 10.x branch: upgrade to 10.0.1 or later