CVE-2021-42983 in Enterprise Client
Summary
by MITRE • 12/07/2021
NoMachine Enterprise Client is affected by Buffer Overflow. IOCTL Handler 0x22001B in the NoMachine Enterprise Client above 4.0.346 and below 7.7.4 allow local attackers to execute arbitrary code in kernel mode or cause a denial of service (memory corruption and OS crash) via specially crafted I/O Request Packet.
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Analysis
by VulDB Data Team • 12/11/2021
The vulnerability CVE-2021-42983 represents a critical buffer overflow flaw within the NoMachine Enterprise Client software ecosystem. This issue affects versions greater than 4.0.346 but prior to 7.7.4, creating a persistent security risk that extends beyond typical user-level applications into the kernel space. The vulnerability manifests through an IOCTL (Input/Output Control) handler identified as 0x22001B, which operates at a privileged level within the Windows kernel environment. The flaw allows local attackers to escalate their privileges and execute arbitrary code with kernel-level permissions, fundamentally compromising system integrity and security boundaries. This type of vulnerability directly violates the principle of least privilege and represents a severe escalation path from local user access to system-level control.
The technical implementation of this buffer overflow occurs within the kernel-mode driver component of the NoMachine Enterprise Client, specifically through improper input validation in the IOCTL handler mechanism. When a specially crafted I/O Request Packet is submitted to the system, the handler fails to properly bounds-check the incoming data before copying it into a fixed-size buffer within kernel memory. This classic buffer overflow condition creates an opportunity for memory corruption that can be exploited to overwrite critical kernel data structures, function pointers, or return addresses. The vulnerability's classification as a kernel-mode exploit places it within the purview of CWE-121, which specifically addresses stack-based buffer overflow conditions, and potentially CWE-122 for heap-based buffer overflows. The attack vector requires local system access, making it a local privilege escalation vulnerability that can be particularly dangerous in environments where multiple users share systems or where untrusted local access exists.
The operational impact of this vulnerability extends beyond simple code execution to encompass complete system compromise and potential denial of service conditions. When exploited successfully, the buffer overflow can cause system crashes, memory corruption, and unpredictable behavior that may result in complete system instability or reboot cycles. The kernel-level nature of the vulnerability means that any successful exploitation can lead to complete system takeover, allowing attackers to install malware, modify system files, or establish persistent backdoors. The vulnerability affects enterprise environments where NoMachine is deployed for remote desktop services, creating a significant risk for organizations that rely on this technology for secure remote access. Organizations using affected versions may experience service disruption, data compromise, or complete system outages, particularly in scenarios where attackers can gain local access through social engineering, compromised accounts, or other attack vectors that lead to local system execution.
Mitigation strategies for CVE-2021-42983 must prioritize immediate patching of affected NoMachine Enterprise Client installations to versions 7.7.4 or later, where the buffer overflow has been addressed through proper bounds checking and input validation. System administrators should implement the principle of least privilege by restricting local access to systems running NoMachine and monitoring for suspicious I/O operations or kernel-level activity. Network segmentation and access controls should be strengthened to limit potential attack surfaces, particularly in enterprise environments where the software may be used for remote desktop services. The vulnerability's characteristics align with ATT&CK technique T1068, which covers local privilege escalation, and T1547.001, covering registry run keys and startup folder modifications. Organizations should also consider implementing kernel-mode exploit detection systems and monitoring for abnormal kernel activity patterns that may indicate exploitation attempts. Regular security assessments and vulnerability scanning should be conducted to identify any remaining instances of affected software within the enterprise environment, ensuring comprehensive protection against this and similar kernel-level vulnerabilities.