CVE-2021-47799: Visual Tools DVR VX16 Privilege Escalation

CVE-2021-47799 Overview

CVE-2021-47799 is a local privilege escalation vulnerability affecting Visual Tools DVR VX16 version 4.2.28. The vulnerability exists in the device's Sudo configuration, which allows authenticated local attackers to escalate privileges to root access. By exploiting unsafe Sudo settings through mount commands to bind a shell, attackers can gain unauthorized system-level privileges on the affected DVR system.

Critical Impact

Successful exploitation allows local attackers to gain full root access on Visual Tools DVR VX16 devices, potentially compromising video surveillance infrastructure and enabling complete system takeover.

Affected Products

• Visual Tools DVR VX16 version 4.2.28

Discovery Timeline

• 2026-01-15 - CVE CVE-2021-47799 published to NVD
• 2026-01-16 - Last updated in NVD database

Technical Details for CVE-2021-47799

Vulnerability Analysis

This vulnerability is classified as CWE-266 (Incorrect Privilege Assignment), where the system fails to properly restrict elevated privileges. The Visual Tools DVR VX16 firmware contains an insecure Sudo configuration that grants users the ability to execute certain commands with elevated privileges without proper validation.

The attack requires local access to the system, meaning an attacker must first have a valid user account or physical access to the device. Once access is obtained, the attacker can leverage the misconfigured Sudo rules to execute mount commands that bind a shell with root privileges. This type of privilege escalation is particularly dangerous in IoT and embedded systems like DVRs, where firmware updates may be infrequent and security configurations are often overlooked.

The vulnerability has a local attack vector, requiring no user interaction and low attack complexity once the attacker has local access with standard user privileges.

Root Cause

The root cause of this vulnerability is an improper Sudo configuration in the Visual Tools DVR VX16 firmware. The Sudo rules permit standard users to execute mount operations without adequate restrictions. This allows attackers to abuse the mount command to bind mount directories containing malicious executables or to bind a shell that inherits elevated privileges.

Embedded devices like DVRs frequently ship with overly permissive configurations to simplify system administration. In this case, the Sudo configuration fails to implement the principle of least privilege, granting capabilities beyond what is necessary for normal device operation.

Attack Vector

The attack follows a local privilege escalation pattern:

1. Initial Access: Attacker gains local access to the DVR system through valid credentials, SSH access, or physical console access
2. Reconnaissance: Attacker enumerates Sudo privileges using sudo -l to identify misconfigured permissions
3. Exploitation: Attacker leverages the permissive mount command to bind a root-owned shell or mount a malicious filesystem
4. Privilege Escalation: Through the bound mount, attacker obtains a shell running with root privileges

The exploitation technique leverages the ability to use mount with the --bind option to create a copy of an existing directory tree at a different mount point, potentially allowing the attacker to overwrite system binaries or gain access to restricted directories with elevated permissions.

For detailed exploitation information, refer to Exploit-DB #50104.

Detection Methods for CVE-2021-47799

Indicators of Compromise

• Unexpected mount operations in system logs, particularly bind mounts targeting /bin, /sbin, or other system directories
• Anomalous Sudo command executions by standard user accounts
• New or modified shell binaries in unexpected locations
• Evidence of privilege escalation such as processes running as root that were spawned from non-privileged user sessions

Detection Strategies

• Monitor Sudo logs (/var/log/auth.log or /var/log/secure) for mount command executions by non-administrative users
• Implement file integrity monitoring on critical system directories to detect unauthorized modifications
• Deploy endpoint detection capabilities to identify privilege escalation patterns on DVR systems
• Review Sudo configuration files (/etc/sudoers and /etc/sudoers.d/) for overly permissive rules

Monitoring Recommendations

• Enable comprehensive logging for Sudo operations and mount system calls
• Configure alerts for any bind mount operations performed through Sudo
• Implement network segmentation to isolate DVR systems and limit potential attacker access
• Deploy SentinelOne agents where supported to provide real-time behavioral analysis and privilege escalation detection

How to Mitigate CVE-2021-47799

Immediate Actions Required

• Audit and restrict Sudo configurations on all Visual Tools DVR VX16 devices running version 4.2.28
• Remove unnecessary Sudo privileges, particularly those allowing mount operations
• Implement network segmentation to limit local access to DVR systems
• Review user accounts and remove any unauthorized or unnecessary local accounts
• Contact Visual Tools for firmware updates or security guidance

Patch Information

No official patch information is available in the CVE data. Organizations should contact Visual Tools directly through their official website for updated firmware or security guidance regarding this vulnerability.

Workarounds

• Modify the Sudoers configuration to remove or restrict mount command permissions for non-administrative users
• Implement strict access controls limiting who can log into the DVR system locally
• Deploy additional monitoring and logging to detect exploitation attempts
• Consider placing affected devices behind additional network access controls until a patch is available

# Example: Restricting Sudo mount permissions
# Review current sudo configuration
sudo visudo

# Remove or comment out any lines granting mount privileges to standard users
# Example of problematic configuration to remove:
# username ALL=(ALL) NOPASSWD: /bin/mount

# Implement principle of least privilege
# Only grant specific, necessary commands with full path restrictions