CVE-2021-33526
📋 TL;DR
This vulnerability allows a low-privileged local attacker to execute arbitrary code with SYSTEM privileges by sending a malicious OpenVPN configuration command to the mbDIALUP service. It affects MB connect line mbDIALUP versions up to 3.9R0.0, putting systems with this software at risk of complete compromise.
💻 Affected Systems
- MB connect line mbDIALUP
📦 What is this software?
Mbdialup by Mbconnectline
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with SYSTEM privileges, allowing attacker to install persistent backdoors, steal credentials, or deploy ransomware across the network.
Likely Case
Local privilege escalation leading to lateral movement within the network, data exfiltration, or deployment of additional malware.
If Mitigated
Limited impact if proper network segmentation and least privilege principles are enforced, though local compromise of affected systems remains possible.
🎯 Exploit Status
Exploitation requires local access but minimal technical skill once the attack vector is understood. The vulnerability is in how the service processes OpenVPN configuration commands.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after 3.9R0.0
Vendor Advisory: https://cert.vde.com/de-de/advisories/vde-2021-017
Restart Required: Yes
Instructions:
1. Download and install the latest version of mbDIALUP from the vendor. 2. Restart the mbDIALUP service. 3. Verify the service is running the patched version.
🔧 Temporary Workarounds
Restrict local user access
windowsLimit which users have local login access to systems running mbDIALUP
Service privilege reduction
windowsRun mbDIALUP service with lower privileges if functionality permits
sc config "mbDIALUP" obj= "NT AUTHORITY\LocalService" type= own
🧯 If You Can't Patch
- Implement strict network segmentation to isolate systems running vulnerable mbDIALUP versions
- Deploy endpoint detection and response (EDR) solutions to monitor for privilege escalation attempts
🔍 How to Verify
Check if Vulnerable:
Check mbDIALUP version in the application interface or via Windows Services (services.msc) looking for mbDIALUP service with version <= 3.9R0.0Check Version:
sc query "mbDIALUP" | findstr /C:"DisplayName"Verify Fix Applied:
Confirm mbDIALUP version is greater than 3.9R0.0 and monitor for successful service restart📡 Detection & Monitoring
Log Indicators:
- Unusual OpenVPN configuration commands sent to mbDIALUP service
- Privilege escalation events from mbDIALUP process
- Unexpected child processes spawned by mbDIALUP service
Network Indicators:
- Unusual outbound connections from systems running mbDIALUP
- Traffic patterns inconsistent with normal OpenVPN usage
SIEM Query:
Process Creation where Parent Process Name contains "mbDIALUP" and Command Line contains unusual OpenVPN parameters