CVE-2021-47814: NBMonitor DoS Vulnerability via Overflow

CVE-2021-47814 Overview

CVE-2021-47814 is a buffer overflow vulnerability (CWE-120) in NBMonitor version 1.6.8 that enables attackers to cause a denial of service condition. The vulnerability exists in the registration code input field, where insufficient bounds checking allows an attacker to crash the application by providing an oversized input buffer. Specifically, pasting a 256-character buffer into the registration key field triggers an application crash and potential system instability.

Critical Impact

Attackers can crash NBMonitor 1.6.8 through a buffer overflow in the registration input field, causing denial of service and potential system instability.

Affected Products

• NBMonitor 1.6.8

Discovery Timeline

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

Technical Details for CVE-2021-47814

Vulnerability Analysis

This vulnerability stems from a classic buffer overflow condition (CWE-120: Buffer Copy without Checking Size of Input) in the registration code validation component of NBMonitor. The application fails to properly validate the length of user-supplied input before copying it into a fixed-size memory buffer. When a user enters or pastes a 256-character string into the registration key field, the input exceeds the allocated buffer size, causing memory corruption that leads to an application crash.

The local attack vector requires user interaction, as an attacker would need to either convince a user to enter the malicious input or have direct access to the application interface. While this vulnerability does not enable code execution or data exfiltration based on available information, it effectively renders the application unusable when triggered.

Root Cause

The root cause is improper input validation in the registration key processing routine. NBMonitor 1.6.8 allocates a fixed-size buffer for the registration code input but does not implement proper boundary checks before copying user-supplied data into this buffer. When input exceeds the expected length (specifically at 256 characters), the application writes beyond the allocated memory region, corrupting adjacent memory and causing the application to crash.

Attack Vector

The attack requires local access to the NBMonitor application interface. An attacker must either have direct access to the system running NBMonitor or socially engineer a user into entering the malicious input. The attack sequence involves:

1. Opening the NBMonitor 1.6.8 registration dialog
2. Pasting or entering a string of 256 or more characters into the registration key field
3. The application crashes due to buffer overflow when processing the oversized input

A proof-of-concept demonstrating this vulnerability is available through the Exploit-DB #49964 entry. Additional technical details can be found in the VulnCheck Advisory on NBMonitor.

Detection Methods for CVE-2021-47814

Indicators of Compromise

• Unexpected NBMonitor application crashes or termination events
• Windows Application Event Log entries indicating buffer overflow or access violation errors for NBMonitor
• Repeated application restarts in short time periods suggesting exploitation attempts
• User reports of application instability when interacting with registration functionality

Detection Strategies

• Monitor Windows Event Logs for application crash events related to NBMonitor with fault codes indicating memory access violations
• Implement endpoint detection rules to identify applications with known vulnerable versions of NBMonitor (version 1.6.8)
• Configure SentinelOne to detect abnormal application termination patterns that may indicate exploitation attempts
• Deploy application inventory solutions to identify systems running the vulnerable NBMonitor version

Monitoring Recommendations

• Enable crash dump collection for NBMonitor to assist in forensic analysis of potential exploitation attempts
• Configure alerts for repeated application crashes within short time windows
• Monitor for any unusual patterns of user interaction with registration dialogs
• Implement SentinelOne's application control features to track vulnerable software installations

How to Mitigate CVE-2021-47814

Immediate Actions Required

• Update NBMonitor to a patched version if one is available from the vendor
• Restrict access to NBMonitor installation to trusted users only
• Consider disabling or restricting access to the registration functionality if not required
• Monitor for any suspicious activity related to the application

Patch Information

Check the NSA Auditor Overview vendor website for updated versions of NBMonitor that address this buffer overflow vulnerability. Organizations should verify that any applied patches resolve the boundary checking issue in the registration input field before deploying to production systems.

Workarounds

• Limit access to the NBMonitor application to only trusted administrators
• Disable or restrict clipboard paste functionality within the application environment if technically feasible
• Implement application whitelisting policies using SentinelOne to control which users can access the vulnerable application
• Consider replacing NBMonitor 1.6.8 with an alternative network monitoring solution until a patch is available