CVE-2023-42365: BusyBox Use-After-Free Vulnerability

CVE-2023-42365 Overview

A use-after-free vulnerability was discovered in BusyBox v.1.36.1 via a crafted awk pattern in the awk.ccopyvar function. This memory corruption flaw allows attackers to potentially cause a denial of service condition by exploiting improper memory handling when processing maliciously crafted awk patterns. The vulnerability requires local access and user interaction to trigger, but successful exploitation can lead to application crashes and system instability.

Critical Impact

Exploitation of this use-after-free vulnerability in BusyBox's awk implementation can cause denial of service through application crashes, affecting embedded systems and Linux distributions that rely on BusyBox utilities.

Affected Products

• BusyBox version 1.36.1
• Linux distributions using vulnerable BusyBox packages
• Embedded systems and IoT devices running BusyBox 1.36.1

Discovery Timeline

• 2023-11-27 - CVE-2023-42365 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2023-42365

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption vulnerability where the application continues to reference memory after it has been freed. In the context of BusyBox's awk implementation, the flaw exists within the copyvar function in awk.c. When processing specially crafted awk patterns, the function improperly handles memory allocation and deallocation, leading to a condition where freed memory is subsequently accessed.

The attack requires local access to the target system and user interaction to process the malicious awk input. While this limits the attack surface compared to remote vulnerabilities, BusyBox's widespread deployment in embedded systems, IoT devices, and minimal Linux environments makes this a significant concern for affected installations.

Root Cause

The root cause of CVE-2023-42365 lies in improper memory management within the copyvar function of BusyBox's awk implementation. The function fails to properly track the lifecycle of memory allocations when copying variable data during awk pattern processing. This results in a scenario where memory is freed prematurely while references to that memory location still exist, creating a use-after-free condition when those dangling references are subsequently accessed.

Attack Vector

The vulnerability is exploited through local access by providing a specially crafted awk pattern to BusyBox's awk applet. An attacker would need to either execute the malicious awk command directly on the target system or convince a user to process a file containing the crafted pattern. The attack does not require elevated privileges but does require user interaction to trigger the vulnerable code path.

The exploitation mechanism involves crafting an awk pattern that triggers specific memory operations within the copyvar function. When the pattern is processed, it causes the function to free memory that is later accessed, resulting in undefined behavior that typically manifests as a crash (denial of service). For detailed technical information about the vulnerability, see the BusyBox Bug Report #15871.

Detection Methods for CVE-2023-42365

Indicators of Compromise

• Unexpected crashes or segmentation faults in BusyBox awk processes
• Core dumps generated by awk-related operations
• Abnormal process termination patterns involving BusyBox utilities
• System logs indicating memory access violations in awk processing

Detection Strategies

• Monitor for BusyBox version 1.36.1 installations across your environment using software inventory tools
• Implement file integrity monitoring for BusyBox binaries to detect unauthorized modifications
• Deploy endpoint detection solutions that can identify exploitation attempts targeting memory corruption vulnerabilities
• Scan embedded systems and IoT devices for vulnerable BusyBox versions during routine security assessments

Monitoring Recommendations

• Configure crash reporting mechanisms to capture and analyze BusyBox-related process failures
• Implement system-level logging to track awk command executions and their parameters
• Set up alerts for unusual patterns of process crashes affecting BusyBox utilities
• Monitor for suspicious awk pattern files or scripts being introduced to systems

How to Mitigate CVE-2023-42365

Immediate Actions Required

• Identify all systems running BusyBox version 1.36.1 in your environment
• Prioritize patching embedded systems and IoT devices that may have longer update cycles
• Consider restricting awk functionality on critical systems where updates cannot be immediately applied
• Review system access controls to limit local access to affected systems

Patch Information

BusyBox maintainers have addressed this vulnerability in subsequent releases. Organizations should update to the latest available BusyBox version that includes the security fix. For Debian-based systems, security updates are available as documented in the Debian LTS Announcement. Consult the BusyBox Bug Report #15871 for additional patch details and version information.

Workarounds

• Disable or remove the awk applet from BusyBox if the functionality is not required for your use case
• Implement strict input validation for any scripts or processes that use BusyBox awk
• Use alternative awk implementations (GNU awk or mawk) on systems where BusyBox awk can be replaced
• Apply access controls to limit which users can execute awk commands on affected systems

# Check BusyBox version to determine if vulnerable
busybox --help | head -n 1

# Verify if awk applet is compiled into BusyBox
busybox --list | grep awk

# On Debian-based systems, check for available updates
apt-get update && apt-cache policy busybox