CVE-2021-42382 in BusyBox
Summary
by MITRE
A use-after-free in Busybox's awk applet leads to denial of service and possibly code execution when processing a crafted awk pattern in the getvar_s function
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 04/24/2025
The vulnerability identified as CVE-2021-42382 represents a critical use-after-free condition within Busybox's awk applet that can result in both denial of service and potential code execution. This flaw exists in the getvar_s function where improper memory management allows attackers to manipulate the execution flow by exploiting freed memory references. The Busybox project serves as a collection of common Unix utilities for embedded systems and Linux environments, making this vulnerability particularly concerning as it affects numerous devices and systems that rely on this foundational software suite. The use-after-free vulnerability occurs when a program continues to reference memory after it has been freed, creating opportunities for malicious code to be executed or system stability to be compromised. This particular issue demonstrates how seemingly benign utility functions can become attack vectors when memory management is not properly enforced.
The technical implementation of this vulnerability stems from inadequate memory handling within the awk applet's getvar_s function which processes variable assignments and manipulations. When processing a crafted awk pattern, the function fails to properly validate or manage memory references, allowing for a scenario where freed memory blocks are accessed after being reallocated. This condition creates a predictable pattern that attackers can exploit to either crash the application through denial of service or potentially execute arbitrary code by manipulating the freed memory contents. The flaw specifically manifests when the awk utility processes malformed input patterns that trigger the getvar_s function with insufficient memory management controls. The vulnerability is classified under CWE-416 as a use-after-free condition, which is a well-documented class of memory safety issues that frequently leads to system compromise and privilege escalation opportunities.
From an operational perspective, this vulnerability presents significant risks across various networked environments where Busybox is deployed, including embedded devices, routers, IoT systems, and containerized environments. The impact extends beyond simple service disruption as the potential for code execution means that attackers could gain unauthorized access to affected systems, particularly in environments where the awk utility is executed with elevated privileges. The exploitation requires crafting specific awk patterns that trigger the vulnerable code path, making it moderately complex but not impossible for skilled attackers to implement. The vulnerability affects multiple versions of Busybox and has been identified in various Linux distributions and embedded systems that utilize this software package. Security researchers have noted that the attack surface is particularly broad due to Busybox's widespread adoption across different device types and operating systems.
Mitigation strategies for CVE-2021-42382 should prioritize immediate patching of affected Busybox versions, with administrators monitoring for updates from their respective distribution vendors. Organizations should implement input validation measures that restrict awk pattern processing to prevent exploitation of the vulnerable function, particularly in environments where untrusted input is processed. Network segmentation and access controls can help limit the potential impact of successful exploitation attempts, while monitoring systems should be configured to detect unusual awk utility behavior. The vulnerability also highlights the importance of proper memory management practices in embedded systems and underscores the need for comprehensive code reviews focusing on memory safety. Security teams should consider implementing runtime protections such as address space layout randomization and stack canaries to make exploitation more difficult, though these measures are not foolproof against sophisticated attacks. Regular vulnerability assessments and penetration testing should include examination of embedded system components to identify similar memory safety issues that could be exploited for similar outcomes.