CVE-2023-42363: BusyBox Use-After-Free Vulnerability

CVE-2023-42363 Overview

A use-after-free vulnerability was discovered in the xasprintf function in xfuncs_printf.c:344 in BusyBox v.1.36.1. This memory corruption vulnerability occurs when the application accesses memory that has already been freed, potentially leading to application crashes and denial of service conditions.

Critical Impact

This use-after-free vulnerability in BusyBox could allow an attacker with local access to cause a denial of service by crashing the application through memory corruption.

Affected Products

• BusyBox v.1.36.1
• Systems and embedded devices utilizing BusyBox xfuncs_printf.c functionality
• IoT devices and embedded Linux systems running vulnerable BusyBox versions

Discovery Timeline

• 2023-11-27 - CVE CVE-2023-42363 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-42363

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption issue that occurs when a program continues to use a pointer after the memory it references has been deallocated. In the context of BusyBox, the vulnerability exists within the xasprintf function located in xfuncs_printf.c at line 344.

Use-after-free vulnerabilities are particularly dangerous in embedded systems like those running BusyBox because they can lead to unpredictable behavior, including crashes, data corruption, or in some cases, code execution. The local attack vector requires user interaction to trigger the vulnerability, which somewhat limits its exploitability but does not eliminate the risk in scenarios where an attacker can influence input to the affected function.

Root Cause

The root cause of this vulnerability lies in improper memory management within the xasprintf function. The function deallocates memory but the application subsequently references that freed memory, resulting in undefined behavior. This typically occurs due to:

• Missing or incorrect pointer nullification after memory deallocation
• Complex control flow paths where memory management state becomes inconsistent
• Race conditions between deallocation and subsequent access attempts

Attack Vector

The attack vector for CVE-2023-42363 is local, requiring an attacker to have local access to the system running BusyBox. The exploitation requires user interaction, suggesting that a victim must open a malicious file or trigger specific input that exercises the vulnerable code path in the xasprintf function.

An attacker could craft malicious input designed to trigger the use-after-free condition, causing the application to crash. While the primary impact is availability (denial of service), use-after-free vulnerabilities can sometimes be escalated to achieve code execution under certain conditions.

The vulnerability exists in the string formatting functionality of BusyBox, which is widely used in embedded systems and IoT devices. Technical details and reproduction steps can be found in the BusyBox Bug Report #15865.

Detection Methods for CVE-2023-42363

Indicators of Compromise

• Unexpected crashes or segmentation faults in BusyBox-based applications
• Core dumps showing memory access violations in xfuncs_printf.c or related functions
• Application logs indicating abnormal termination of BusyBox utilities

Detection Strategies

• Implement file integrity monitoring on BusyBox binaries to detect unauthorized modifications
• Monitor for unusual application crashes or restarts in systems running BusyBox v.1.36.1
• Deploy runtime memory protection tools that can detect use-after-free conditions
• Use AddressSanitizer (ASan) during development and testing to identify memory corruption issues

Monitoring Recommendations

• Configure system logging to capture application crashes with stack traces
• Monitor embedded devices and IoT systems for unexpected reboots or service interruptions
• Implement automated alerting for patterns consistent with denial of service attacks
• Track BusyBox process stability metrics across affected infrastructure

How to Mitigate CVE-2023-42363

Immediate Actions Required

• Inventory all systems running BusyBox v.1.36.1 and prioritize them for remediation
• Review and apply available patches from the BusyBox project
• Implement network segmentation for affected embedded devices where immediate patching is not feasible
• Restrict local access to systems running vulnerable BusyBox versions

Patch Information

The vulnerability has been reported to the BusyBox project through Bug Report #15865. Organizations should monitor the BusyBox project for official patches and upgrade to a version that addresses this vulnerability when available.

For embedded systems and IoT devices, contact the device manufacturer for firmware updates that include patched versions of BusyBox.

Workarounds

• Limit local access to systems running BusyBox to trusted users only
• Implement application-level input validation to filter potentially malicious input before it reaches BusyBox functions
• Deploy memory protection mechanisms such as ASLR and DEP where supported by the platform
• Consider replacing BusyBox with alternative implementations in critical systems until a patch is available

# Configuration example - Verify BusyBox version
busybox --help | head -n 1
# Output will show current version

# Check for vulnerable version
if busybox --help 2>&1 | grep -q "1.36.1"; then
    echo "WARNING: Vulnerable BusyBox version detected"
fi