CVE-2021-47813: Backup Key Recovery DoS Vulnerability

CVE-2021-47813 Overview

CVE-2021-47813 is a buffer overflow vulnerability in Backup Key Recovery version 2.2.7 that enables attackers to cause a denial of service condition. The vulnerability exists in the registration code input field, where improper boundary checking allows an attacker to overflow the buffer by pasting an excessively large input (256 repeated characters), resulting in application instability and potential crash.

Critical Impact

Local attackers can crash the Backup Key Recovery application by exploiting the registration key input field, causing complete loss of application availability.

Affected Products

• Backup Key Recovery 2.2.7
• NSAuditor Software - Backup Key Recovery

Discovery Timeline

• 2026-01-16 - CVE CVE-2021-47813 published to NVD
• 2026-01-16 - Last updated in NVD database

Technical Details for CVE-2021-47813

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), a classic buffer overflow condition. The application fails to properly validate the length of user-supplied input in the registration code field before copying it to a fixed-size buffer. When a user pastes a specially crafted string containing 256 or more repeated characters into this field, the application's buffer is overflowed, leading to memory corruption.

The local attack vector requires user interaction—specifically, a user must be tricked into pasting malicious input or the attacker must have local access to the system. While this vulnerability results in high availability impact through application crashes, it does not compromise confidentiality or integrity of data.

Root Cause

The root cause is improper input validation in the registration key handling routine. The application allocates a fixed-size buffer for the registration code input but does not enforce length restrictions before copying user-supplied data into this buffer. This allows oversized input to overwrite adjacent memory locations, corrupting the application's memory state and causing instability or crashes.

Attack Vector

The attack requires local access to the target system where Backup Key Recovery 2.2.7 is installed. An attacker can exploit this vulnerability by:

1. Opening the Backup Key Recovery application
2. Navigating to the registration or license key input dialog
3. Pasting a buffer containing 256 repeated characters (e.g., "A" x 256)
4. The application processes this oversized input, triggering the buffer overflow
5. The application becomes unstable and crashes

The vulnerability has been documented with a proof-of-concept available through Exploit-DB #49966. Additional technical details can be found in the VulnCheck Advisory.

Detection Methods for CVE-2021-47813

Indicators of Compromise

• Unexpected crashes of the Backup Key Recovery application, particularly during registration attempts
• Windows Event Log entries indicating application faults in the Backup Key Recovery process
• Evidence of unusually long text strings in clipboard history or input logs

Detection Strategies

• Monitor application crash events for Backup Key Recovery using Windows Event Viewer
• Implement endpoint detection rules that alert on repeated application crashes within short time windows
• Deploy SentinelOne Singularity to detect abnormal application behavior and crash patterns indicative of exploitation attempts

Monitoring Recommendations

• Enable detailed application logging for Backup Key Recovery if available
• Configure endpoint protection to monitor for buffer overflow exploitation patterns
• Review system event logs regularly for signs of denial of service attacks against desktop applications

How to Mitigate CVE-2021-47813

Immediate Actions Required

• Upgrade Backup Key Recovery to a patched version if one is available from the vendor
• Restrict access to systems running vulnerable versions of the software
• Educate users about the risks of pasting untrusted content into application input fields
• Consider removing or disabling the application if it is not critical to operations

Patch Information

No vendor patch information is currently available in the CVE data. Organizations should monitor the NSAuditor website for security updates addressing this vulnerability.

Workarounds

• Limit local user access to machines running the vulnerable application
• Implement application whitelisting to prevent unauthorized execution of the software
• Use endpoint protection solutions like SentinelOne to detect and prevent exploitation attempts
• Consider deploying network segmentation to isolate systems running legacy software with known vulnerabilities