CVE-2021-47814: Nsasoft NBMonitor DOS Vulnerability

CVE-2021-47814 Overview

CVE-2021-47814 is a denial of service vulnerability in Nsasoft NBMonitor version 1.6.8. The flaw exists in the application's registration code input field, which fails to validate input length before processing. Attackers with local access can paste a 256-character buffer into the registration key field, causing the application to crash. The vulnerability is categorized under [CWE-120] Buffer Copy without Checking Size of Input. While the attack requires user interaction and local access, successful exploitation results in application unavailability and potential system instability on the affected host.

Critical Impact
Local attackers can crash NBMonitor 1.6.8 by submitting an oversized 256-character buffer to the registration key field, resulting in denial of service.

Affected Products

Nsasoft NBMonitor 1.6.8
cpe:2.3:a:nsasoft:nbmonitor:1.6.8:*:*:*:*:*:*:*
Windows hosts running the vulnerable NBMonitor build

Discovery Timeline

2026-01-16 - CVE-2021-47814 published to NVD
2026-01-29 - Last updated in NVD database

Technical Details for CVE-2021-47814

Vulnerability Analysis

NBMonitor 1.6.8 is a network monitoring utility from Nsasoft. The application exposes a registration interface where users enter a license key to activate the software. This input field does not enforce length validation on pasted content. When an attacker submits a 256-character string, the underlying buffer handling logic fails and the application terminates unexpectedly.

The vulnerability is classified as [CWE-120], a classic buffer copy without input size checking. The attack requires local access and user interaction, limiting remote exploitation. The EPSS score reflects very low observed exploitation activity in the wild. Public proof-of-concept code exists in Exploit-DB entry 49964, lowering the barrier for opportunistic abuse on shared workstations or kiosk-style deployments.

Root Cause

The root cause is missing input length validation on the registration code field. The application accepts arbitrarily long input from the clipboard without enforcing a maximum character limit. When the oversized buffer reaches internal string handling routines, memory corruption or unhandled exceptions cause the process to terminate.

Attack Vector

Exploitation requires local access to a host running NBMonitor 1.6.8. The attacker opens the registration dialog, pastes a crafted 256-character payload into the key field, and submits it. The application crashes immediately. No elevated privileges are required, but a user must interact with the registration interface. The impact is limited to availability of the NBMonitor process and any monitoring tasks it performs.

Technical details and a working proof-of-concept are documented in the Exploit-DB #49964 entry and the VulnCheck Advisory on nbmonitor.

Detection Methods for CVE-2021-47814

Indicators of Compromise

Repeated nbmonitor.exe process crashes recorded in Windows Application event logs with faulting module references.
Windows Error Reporting (WER) entries citing nbmonitor.exe with exception codes such as 0xC0000005 or 0xC0000409.
Presence of NBMonitor 1.6.8 binaries on endpoints inventoried as cpe:2.3:a:nsasoft:nbmonitor:1.6.8.

Detection Strategies

Hunt for abnormal termination events of nbmonitor.exe correlated with interactive user sessions.
Monitor for clipboard paste operations followed by application crashes on hosts running monitoring tools.
Inventory endpoints for installed Nsasoft NBMonitor versions and flag any instance at or below 1.6.8.

Monitoring Recommendations

Forward Windows Application and WER event logs to a central SIEM for crash pattern analysis.
Alert on process exit codes that indicate unhandled exceptions in monitoring utilities.
Track installations of legacy Nsasoft utilities through software inventory scans.

How to Mitigate CVE-2021-47814

Immediate Actions Required

Identify all hosts running NBMonitor 1.6.8 and restrict interactive access to trusted administrators.
Remove or replace NBMonitor 1.6.8 where the registration interface is exposed to multiple users.
Apply application control policies to prevent execution of the vulnerable build on shared systems.

Patch Information

No vendor advisory or fixed version has been published in the referenced sources at the time of NVD publication. Consult the NSA Auditor Tool Overview for any updated releases from Nsasoft and replace NBMonitor 1.6.8 with a supported version when available.

Workarounds

Avoid opening the registration dialog on production hosts and complete licensing in a controlled environment.
Restrict local logon rights on systems running NBMonitor to reduce the population of users who can trigger the crash.
Use application allowlisting to block the vulnerable nbmonitor.exe binary if the tool is not business-critical.

bash

# Example: Remove NBMonitor 1.6.8 via PowerShell on Windows
Get-WmiObject -Class Win32_Product -Filter "Name LIKE '%NBMonitor%'" | ForEach-Object { $_.Uninstall() }