CVE-2021-42385 is a high-severity vulnerability identified in the BusyBox software suite, specifically within its awk applet. BusyBox is a widely used software package that provides several Unix utilities in a single executable, commonly deployed in embedded systems, routers, IoT devices, and lightweight Linux distributions. The vulnerability is classified as a use-after-free (CWE-416) issue occurring in the evaluate function when processing a crafted awk pattern. A use-after-free flaw arises when a program continues to use memory after it has been freed, which can lead to undefined behavior including crashes or arbitrary code execution. In this case, the vulnerability can lead to denial of service (DoS) by crashing the affected process, and potentially to remote code execution (RCE) if an attacker can control the input to the awk applet. The CVSS 3.1 base score is 7.2, indicating a high severity level. The vector string (AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H) shows that the attack requires network access, low attack complexity, but requires high privileges (PR:H) and no user interaction (UI:N). The scope is unchanged (S:U), and the impact on confidentiality, integrity, and availability is high. No known exploits in the wild have been reported as of the published date (November 2021). The affected versions are unspecified, but given BusyBox’s widespread use, many embedded and Linux-based systems could be vulnerable if not patched. The lack of patch links suggests that users should consult official BusyBox repositories or vendor advisories for updates. The vulnerability’s root cause is in the memory management of the awk applet’s evaluate function, which processes patterns and scripts. An attacker able to supply crafted awk patterns to a privileged BusyBox instance could trigger this flaw.

For European organizations, the impact of CVE-2021-42385 can be significant, especially for those relying on embedded devices, network appliances, or lightweight Linux distributions that include BusyBox. The vulnerability’s requirement for high privileges means that exploitation typically requires prior access or elevated permissions, limiting remote exploitation but increasing risk in environments where internal threat actors or compromised accounts exist. Successful exploitation could lead to denial of service, disrupting critical network infrastructure or embedded systems, and potentially allow code execution, enabling attackers to escalate privileges, persist in the environment, or pivot to other systems. This is particularly concerning for sectors with critical infrastructure such as telecommunications, energy, manufacturing, and transportation, which often use embedded devices running BusyBox. The potential for code execution elevates the risk to confidentiality and integrity of sensitive data and operational processes. Additionally, denial of service could impact availability of essential services. Given the widespread deployment of BusyBox in IoT and embedded devices, many European organizations may have vulnerable assets that are difficult to patch promptly, increasing exposure. The absence of known exploits in the wild reduces immediate risk but does not eliminate the threat, as attackers may develop exploits over time.

1. Immediate patching: Organizations should identify all systems running BusyBox, particularly those exposing the awk applet, and apply the latest BusyBox updates or patches from trusted sources. 2. Privilege restriction: Since exploitation requires high privileges, enforce strict access controls and minimize the number of users or processes with elevated permissions on devices running BusyBox. 3. Input validation and filtering: Where possible, restrict or sanitize inputs that can be passed to the awk applet, especially on network-facing services or scripts that invoke BusyBox awk. 4. Network segmentation: Isolate embedded devices and IoT systems running BusyBox from critical network segments to limit attacker lateral movement if exploitation occurs. 5. Monitoring and detection: Implement logging and anomaly detection focused on BusyBox usage patterns, especially unusual invocations of the awk applet or crashes that may indicate exploitation attempts. 6. Vendor coordination: Engage with device vendors and suppliers to confirm patch availability and timelines, and request firmware updates where BusyBox is embedded. 7. Incident response readiness: Prepare for potential denial of service or code execution incidents by having response plans and backups for affected systems. 8. Alternative tools: Where feasible, replace BusyBox awk usage with more secure or updated utilities that do not contain this vulnerability, especially in critical environments.