CVE-2023-42364: BusyBox Use-After-Free Vulnerability

CVE-2023-42364 Overview

A use-after-free vulnerability has been identified in BusyBox v.1.36.1 that allows attackers to cause a denial of service through a specially crafted AWK pattern. The vulnerability exists within the evaluate function in awk.c, where improper memory management leads to accessing freed memory when processing malicious AWK patterns.

Critical Impact

Attackers can crash BusyBox processes by providing maliciously crafted AWK patterns, potentially disrupting embedded systems and IoT devices that rely on BusyBox utilities for core functionality.

Affected Products

• BusyBox 1.36.1
• Systems utilizing BusyBox AWK implementation
• Embedded Linux distributions incorporating affected BusyBox versions

Discovery Timeline

• 2023-11-27 - CVE-2023-42364 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2023-42364

Vulnerability Analysis

This use-after-free vulnerability (CWE-416) occurs in the AWK implementation within BusyBox, specifically in the evaluate function located in awk.c. Use-after-free vulnerabilities arise when a program continues to use a pointer after the memory it references has been freed. In this case, the AWK pattern parser fails to properly track memory allocations during pattern evaluation, leading to a scenario where freed memory is subsequently accessed.

The vulnerability requires local access and user interaction, as an attacker must convince a user or automated process to execute AWK commands with a maliciously crafted pattern. When triggered, the vulnerability causes the BusyBox process to crash, resulting in a denial of service condition. This is particularly impactful in embedded systems and IoT environments where BusyBox serves as the foundation for many core utilities.

Root Cause

The root cause lies in improper memory lifecycle management within the evaluate function of awk.c. During AWK pattern processing, certain memory allocations are freed prematurely while references to that memory are still held and subsequently used. This creates a dangling pointer scenario where the program attempts to access memory that has already been returned to the system's memory allocator.

Attack Vector

The attack requires local access to the system and involves providing a specially crafted AWK pattern to the BusyBox AWK utility. The attacker must craft an AWK pattern that triggers the specific code path in the evaluate function where the use-after-free condition exists.

The vulnerability manifests when processing malicious AWK patterns through the evaluate function in awk.c. The crafted pattern triggers improper memory management, causing the program to access freed memory. For technical details on the specific pattern structure that triggers this vulnerability, see the BusyBox Bug Report #15868.

Detection Methods for CVE-2023-42364

Indicators of Compromise

• Unexpected crashes or segmentation faults in BusyBox AWK processes
• Core dumps generated by AWK operations with unusual pattern inputs
• System logs showing repeated AWK process terminations
• Abnormal memory access patterns in BusyBox-related processes

Detection Strategies

• Monitor for AWK process crashes and unexpected terminations on systems running vulnerable BusyBox versions
• Implement input validation for AWK patterns processed from untrusted sources
• Deploy memory debugging tools like AddressSanitizer during testing to detect use-after-free conditions
• Review application logs for patterns of denial of service against BusyBox utilities

Monitoring Recommendations

• Configure system monitoring to alert on repeated crashes of BusyBox utilities
• Implement process health monitoring for critical embedded systems using BusyBox
• Track core dump generation rates for early warning of potential exploitation attempts
• Monitor resource utilization patterns that may indicate DoS attacks targeting AWK functionality

How to Mitigate CVE-2023-42364

Immediate Actions Required

• Identify all systems running BusyBox version 1.36.1 and prioritize them for patching
• Review and restrict access to AWK functionality from untrusted input sources
• Implement input validation for AWK patterns in applications that process external data
• Consider temporarily disabling AWK functionality in security-critical embedded systems until patches can be applied

Patch Information

Updates addressing this vulnerability are available through distribution channels. Debian LTS users should refer to the Debian LTS Announcement January 2025 for specific patch information. For other distributions, consult your vendor's security advisories or the BusyBox Bug Report #15868 for upstream fix details.

Workarounds

• Restrict AWK functionality to trusted users and processes only
• Implement strict input validation to filter potentially malicious AWK patterns before processing
• Use alternative AWK implementations (such as gawk or mawk) if available and appropriate for your environment
• Deploy process isolation and sandboxing for BusyBox utilities handling untrusted input

# Configuration example - Restrict AWK access permissions
# Limit BusyBox AWK execution to trusted users
chmod 750 /bin/busybox
chown root:trusted-users /bin/busybox

# Create a wrapper script with input validation
# This example rejects patterns with potentially dangerous constructs