CVE-2023-7216: GNU Cpio Path Traversal Vulnerability

CVE-2023-7216 Overview

A path traversal vulnerability was found in the CPIO utility. This issue could allow a remote unauthenticated attacker to trick a user into opening a specially crafted archive. During the extraction process, the archiver could follow symlinks outside of the intended directory, which allows files to be written in arbitrary directories through symlinks.

Critical Impact

Attackers can write arbitrary files to system directories by exploiting symlink following during CPIO archive extraction, potentially leading to system compromise or data manipulation.

Affected Products

• GNU CPIO (all versions)
• Red Hat Enterprise Linux 7.0
• Red Hat Enterprise Linux 8.0
• Red Hat Enterprise Linux 9.0

Discovery Timeline

• 2024-02-05 - CVE CVE-2023-7216 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-7216

Vulnerability Analysis

This vulnerability is classified as CWE-22 (Improper Limitation of a Pathname to a Restricted Directory), commonly known as Path Traversal. The CPIO utility fails to properly validate symbolic links within archive files during the extraction process. When a user extracts a maliciously crafted CPIO archive, the utility blindly follows symlinks contained within the archive without verifying whether those symlinks point to locations outside the intended extraction directory.

The attack requires local access and user interaction—specifically, the victim must be tricked into extracting a specially crafted archive file. While this increases the barrier to exploitation, the impact can be significant as it allows arbitrary file writes to any location accessible by the user running the CPIO command.

Root Cause

The root cause stems from insufficient validation of symlink targets during archive extraction. The CPIO utility processes symlinks contained in archive files without checking whether the resolved path escapes the intended extraction directory. This allows an attacker to craft an archive containing a symlink pointing to a sensitive system location (such as /etc/passwd or user configuration files), followed by a file that gets written through that symlink.

Attack Vector

The attack requires the following conditions to be successful:

1. An attacker creates a malicious CPIO archive containing a symlink that points outside the extraction directory (e.g., ../../../etc/cron.d/)
2. The archive also contains a file that will be written through this symlink
3. The victim downloads or receives this malicious archive
4. The victim extracts the archive using the cpio command
5. Due to improper path validation, the file is written to the attacker-controlled location outside the intended directory

This type of symlink-following vulnerability during extraction is often referred to as a "Zip Slip" variant attack, adapted to the CPIO archive format. The attacker can potentially overwrite configuration files, inject malicious scripts into startup directories, or manipulate application data.

Detection Methods for CVE-2023-7216

Indicators of Compromise

• Unexpected files appearing in system directories after CPIO archive extraction operations
• Symlinks within extracted archives pointing to locations outside the extraction directory
• Modified system configuration files that coincide with CPIO extraction activity
• Suspicious CPIO archives received from untrusted sources containing symlinks

Detection Strategies

• Monitor cpio command execution with arguments that indicate extraction operations (-i, --extract)
• Implement file integrity monitoring on critical system directories to detect unauthorized modifications
• Use archive scanning tools to inspect CPIO files for suspicious symlinks before extraction
• Configure audit logging to track file creation events in sensitive directories

Monitoring Recommendations

• Enable system auditing for the cpio binary execution using auditd rules
• Monitor for symlink creation in temporary directories followed by file writes to system paths
• Implement centralized logging for all archive extraction operations across enterprise systems
• Set up alerts for any modifications to critical configuration files in /etc/ and user home directories

How to Mitigate CVE-2023-7216

Immediate Actions Required

• Avoid extracting CPIO archives from untrusted or unknown sources
• Use the --no-absolute-filenames option when extracting CPIO archives to prevent absolute path extraction
• Extract archives in isolated environments or containers when dealing with untrusted content
• Review and apply vendor patches when available from Red Hat and GNU

Patch Information

Organizations running affected versions should consult the Red Hat CVE-2023-7216 Advisory for official patch information and updates. Additional technical details and tracking information can be found in Red Hat Bugzilla Report #2249901.

Administrators should subscribe to security announcement mailing lists for Red Hat Enterprise Linux and GNU CPIO to receive timely notifications of security updates.

Workarounds

• Use alternative archive extraction tools that implement proper symlink validation (e.g., bsdcpio with safe extraction modes)
• Implement a pre-extraction validation script that scans CPIO archives for suspicious symlinks before extraction
• Run CPIO extraction operations in a sandboxed environment using tools like firejail or container isolation
• Configure file system permissions to restrict write access to sensitive directories for non-privileged users

# Safe extraction practices for CPIO archives
# Extract to a dedicated directory with restricted permissions
mkdir -p /tmp/cpio-extract-$(date +%s)
cd /tmp/cpio-extract-*

# Use --no-absolute-filenames to prevent absolute path extraction
cpio -idv --no-absolute-filenames < archive.cpio

# Verify extracted contents before moving to intended location
find . -type l -exec ls -la {} \;