CVE-2021-42383 – CVE-2021-42383 is a use-after-free vulnerabilit... (How to Fix)

Q: What is the severity of CVE-2021-42383?

CVE-2021-42383 has a CVSS score of 7.2 (HIGH). CVE-2021-42383 is a use-after-free vulnerability in BusyBox's awk applet that can be triggered by processing a specially crafted awk pattern. This vulnerability allows denial of service and potentially remote code execution. It affects any system using vulnerable versions of BusyBox with the awk applet enabled.

📋 TL;DR

CVE-2021-42383 is a use-after-free vulnerability in BusyBox's awk applet that can be triggered by processing a specially crafted awk pattern. This vulnerability allows denial of service and potentially remote code execution. It affects any system using vulnerable versions of BusyBox with the awk applet enabled.

💻 Affected Systems

Products:

BusyBox

Versions: BusyBox versions before 1.34.0

Operating Systems: Linux, Embedded Linux systems, Android, IoT devices

Default Config Vulnerable: ⚠️ Yes

Notes: Only vulnerable if the awk applet is included in the BusyBox build (common in default configurations).

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with the privileges of the BusyBox process, potentially leading to full system compromise.

🟠

Likely Case

Denial of service causing BusyBox awk to crash, disrupting scripts and services that rely on it.

🟢

If Mitigated

Limited impact if BusyBox runs with minimal privileges and proper sandboxing/isolation.

🌐 Internet-Facing: MEDIUM - Exploitation requires processing attacker-controlled input, but many internet-facing systems use BusyBox for lightweight utilities.

🏢 Internal Only: MEDIUM - Internal systems using BusyBox awk in scripts or automation could be vulnerable to privilege escalation.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires crafting a malicious awk pattern and getting it processed by BusyBox awk. Public proof-of-concept code exists.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: BusyBox 1.34.0 and later

Vendor Advisory: https://git.busybox.net/busybox/commit/?id=bd4c4a9d6c296c07c5c1ff0d21d0d9dac4c5d2a7

Restart Required: No

Instructions:

1. Update BusyBox to version 1.34.0 or later. 2. Recompile BusyBox if using custom builds. 3. Replace existing BusyBox binary with patched version. 4. No system restart needed, but restart affected services.

🔧 Temporary Workarounds

Disable awk applet

linux

Remove awk functionality from BusyBox build to eliminate attack surface.

Recompile BusyBox with awk applet disabled using 'make menuconfig' or similar.

Use standalone awk

linux

Replace BusyBox awk with GNU awk or other standalone awk implementation.

apt-get install gawk
yum install gawk
apk add gawk

🧯 If You Can't Patch

Restrict access to BusyBox awk to trusted users only.
Implement strict input validation for any data processed by BusyBox awk.

🔍 How to Verify

Check if Vulnerable:

Check BusyBox version: busybox | head -1. If version is before 1.34.0 and includes awk, it's vulnerable.

Check Version:

busybox | head -1

Verify Fix Applied:

Verify BusyBox version is 1.34.0 or later: busybox | head -1. Test with known malicious patterns if possible.

📡 Detection & Monitoring

Log Indicators:

BusyBox awk process crashes
Segmentation faults in awk-related processes
Unexpected awk pattern processing

Network Indicators:

Unusual network traffic containing awk patterns to systems running BusyBox

SIEM Query:

Process:Name='busybox' AND CommandLine CONTAINS 'awk' AND (EventID=1000 OR Signal='SIGSEGV')

📊 Metadata

CVE ID: CVE-2021-42383

CVSS v3 Score: 7.2 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-416

Published: November 15, 2021

Last Updated: April 23, 2025

🔗 References

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🔗 Related Vulnerabilities

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