CVE-2021-47829: DHCP Broadband Privilege Escalation Flaw

CVE-2021-47829 Overview

CVE-2021-47829 is an unquoted service path vulnerability affecting DHCP Broadband 4.1.0.1503. This vulnerability exists in the service configuration where the executable path C:\Program Files\DHCP Broadband 4\dhcpt.exe is not properly quoted. Local attackers can exploit this flaw to execute arbitrary code with elevated privileges by placing a malicious executable in a location that Windows will execute before the legitimate service binary.

Critical Impact

Local attackers can achieve privilege escalation to LocalSystem permissions by exploiting the unquoted service path, potentially gaining complete control over the affected system.

Affected Products

• DHCP Broadband 4.1.0.1503

Discovery Timeline

• 2026-01-16 - CVE CVE-2021-47829 published to NVD
• 2026-01-16 - Last updated in NVD database

Technical Details for CVE-2021-47829

Vulnerability Analysis

This vulnerability is classified as CWE-428 (Unquoted Search Path or Element). When Windows services are configured with executable paths that contain spaces but are not enclosed in quotation marks, the operating system's path parsing behavior creates an exploitable condition. Windows attempts to locate the executable by sequentially testing path segments at each space character.

For the path C:\Program Files\DHCP Broadband 4\dhcpt.exe, Windows will attempt to execute files in the following order:

1. C:\Program.exe
2. C:\Program Files\DHCP.exe
3. C:\Program Files\DHCP Broadband 4\dhcpt.exe

If an attacker has write access to C:\ or C:\Program Files\, they can place a malicious executable named Program.exe or DHCP.exe that will be executed with the service's privileges before the legitimate binary is reached.

Root Cause

The root cause is improper configuration of the Windows service registry entry for the DHCP Broadband service. The ImagePath value in the Windows registry does not include quotation marks around the path containing spaces. This is a common misconfiguration in Windows service installations that can lead to privilege escalation when combined with weak file system permissions.

Attack Vector

The attack requires local access to the system with the ability to write files to directories in the service's unquoted path. An attacker would:

1. Identify the vulnerable unquoted service path in the Windows registry
2. Determine which directories in the path are writable
3. Place a malicious executable with an appropriate name (e.g., Program.exe or DHCP.exe)
4. Wait for or trigger a service restart
5. The malicious code executes with LocalSystem privileges when the service starts

The vulnerability requires local access and low privileges to exploit, but no user interaction is needed once the malicious file is in place. The service typically runs at system startup or can be restarted by an administrator, at which point the attacker's code will execute with elevated privileges.

Detection Methods for CVE-2021-47829

Indicators of Compromise

• Presence of unexpected executables named Program.exe or DHCP.exe in the root of C:\ or C:\Program Files\
• Unusual process execution chains where service host processes spawn unexpected child processes
• Modification timestamps on system directories indicating recent file creation
• Registry modifications to service configurations

Detection Strategies

• Monitor for file creation events in C:\ and C:\Program Files\ directories for executables matching common unquoted path exploitation patterns
• Implement registry monitoring for changes to service ImagePath values that remove quotation marks
• Use Windows Event Log analysis to detect service start failures or unexpected service behavior
• Deploy endpoint detection rules that alert on known unquoted service path exploitation techniques

Monitoring Recommendations

• Enable Windows Security Event logging for process creation (Event ID 4688) with command line auditing
• Configure file integrity monitoring on system directories where malicious executables could be placed
• Implement Sysmon logging to capture detailed process creation and file creation events
• Establish baseline behavior for the DHCP Broadband service to detect anomalous activity

How to Mitigate CVE-2021-47829

Immediate Actions Required

• Audit the Windows registry for the DHCP Broadband service configuration and manually add quotation marks around the ImagePath value
• Review file system permissions on C:\ and C:\Program Files\ to ensure non-administrative users cannot create files
• Check for any suspicious executables in directories along the unquoted path
• Consider temporarily disabling the vulnerable service if not critical to operations until properly remediated

Patch Information

Contact the vendor Weird Solutions for an updated installer that properly quotes the service path during installation. Additional technical details are available in the VulnCheck Advisory and Exploit-DB #49850.

Workarounds

• Manually correct the registry entry by adding quotation marks around the full path in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\<ServiceName>\ImagePath
• Restrict write permissions on C:\ and C:\Program Files\ directories to administrators only
• Implement application whitelisting to prevent unauthorized executables from running
• Use Windows Defender Application Control (WDAC) or AppLocker policies to block execution of unauthorized binaries in system directories

# Registry fix example (run as Administrator in PowerShell)
# First, backup the current value, then set the corrected quoted path
$regPath = "HKLM:\SYSTEM\CurrentControlSet\Services\DHCPBroadband"
Set-ItemProperty -Path $regPath -Name "ImagePath" -Value '"C:\Program Files\DHCP Broadband 4\dhcpt.exe"'