CVE-2024-39943 is a critical OS command injection vulnerability affecting rejetto HFS (HTTP File Server) versions prior to 0.52.10 on Linux, UNIX, and macOS platforms. The vulnerability stems from the server's use of Node.js's execSync function to execute the 'df' command, which is used to report disk space usage. Instead of using the safer spawnSync method, execSync invokes a shell, allowing an attacker with Upload permissions to inject arbitrary commands. This means that any authenticated user who can upload files can craft payloads that execute arbitrary system commands with the privileges of the HFS process. The vulnerability is classified under CWE-284 (Improper Access Control) because it requires authentication but exploits insufficient validation and unsafe command execution. The CVSS 3.1 score of 9.9 reflects the vulnerability's critical nature, with network attack vector, low attack complexity, no user interaction, and scope change. The impact includes full system compromise, data theft, service disruption, or lateral movement within the network. Although no public exploits have been reported yet, the severity and ease of exploitation make it a high priority for remediation. The vulnerability affects multiple UNIX-like operating systems, increasing its potential reach across diverse environments.

The impact of CVE-2024-39943 is severe for organizations using vulnerable versions of rejetto HFS on Linux, UNIX, or macOS. Successful exploitation allows remote authenticated users with Upload permissions to execute arbitrary OS commands, potentially leading to full system compromise. This can result in unauthorized data access or exfiltration, disruption or destruction of services, installation of persistent malware, and lateral movement within corporate networks. Given the critical CVSS score and the fact that exploitation requires only low-level authentication, attackers who gain upload access can escalate privileges and control affected servers. This threatens confidentiality, integrity, and availability of critical systems and data. Organizations relying on HFS for file sharing or web services are at risk, especially if upload permissions are broadly assigned or if authentication mechanisms are weak. The vulnerability could be leveraged in targeted attacks against enterprises, government agencies, or service providers using HFS, leading to significant operational and reputational damage.

To mitigate CVE-2024-39943, organizations should immediately upgrade rejetto HFS to version 0.52.10 or later, where the vulnerability is fixed by replacing execSync with spawnSync to safely execute system commands. If patching is not immediately possible, restrict Upload permissions to only fully trusted users and audit existing permissions to minimize exposure. Implement strict input validation and sanitization on any user-supplied data that might be used in command execution contexts. Employ network segmentation and firewall rules to limit access to HFS servers, especially from untrusted networks. Monitor logs for unusual command execution patterns or unauthorized uploads. Consider deploying application-layer firewalls or runtime application self-protection (RASP) solutions to detect and block command injection attempts. Regularly review and update authentication mechanisms to ensure strong, multi-factor authentication is enforced for users with upload rights. Finally, conduct security awareness training for administrators and users about the risks of granting upload permissions and the importance of applying security patches promptly.