CVE-2021-33527
📋 TL;DR
CVE-2021-33527 is a critical input validation vulnerability in MB connect line mbDIALUP software that allows remote attackers to execute arbitrary code with SYSTEM privileges. This affects all versions up to 3.9R0.0, enabling complete system compromise. Organizations using this dial-up connectivity software are at immediate risk.
💻 Affected Systems
- MB connect line mbDIALUP
📦 What is this software?
Mbdialup by Mbconnectline
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with attacker gaining SYSTEM privileges, enabling data theft, ransomware deployment, lateral movement, and persistent backdoor installation.
Likely Case
Remote code execution leading to service disruption, credential harvesting, and installation of malware or cryptocurrency miners.
If Mitigated
Limited impact if network segmentation prevents external access and strict firewall rules block unnecessary traffic to the service.
🎯 Exploit Status
The vulnerability requires sending a specifically crafted HTTP request to the vulnerable service, which is relatively straightforward for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions > 3.9R0.0
Vendor Advisory: https://cert.vde.com/de-de/advisories/vde-2021-017
Restart Required: Yes
Instructions:
1. Download the latest version from MB connect line vendor portal. 2. Backup current configuration. 3. Install the update following vendor instructions. 4. Restart the service/system. 5. Verify the update was successful.
🔧 Temporary Workarounds
Network Segmentation and Firewall Rules
windowsBlock external and unnecessary internal access to the mbDIALUP HTTP service port
netsh advfirewall firewall add rule name="Block mbDIALUP" dir=in action=block protocol=TCP localport=[PORT_NUMBER]
Service Account Privilege Reduction
windowsChange the service to run with lower privileges if business requirements allow
sc config "mbDIALUP" obj= "NT AUTHORITY\LocalService" password= ""
🧯 If You Can't Patch
- Implement strict network segmentation to isolate affected systems from untrusted networks
- Deploy application control/whitelisting to prevent execution of unauthorized code
🔍 How to Verify
Check if Vulnerable:
Check the installed version of mbDIALUP software. If version is 3.9R0.0 or earlier, the system is vulnerable.Check Version:
Check the software version in the mbDIALUP administration interface or examine the installed program version in Windows Programs and FeaturesVerify Fix Applied:
Verify the installed version is greater than 3.9R0.0 and test that the HTTP service responds normally to legitimate requests.📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP requests to mbDIALUP service port
- Service crashes or unexpected restarts
- Unusual process creation from the mbDIALUP service
Network Indicators:
- HTTP requests with unusual patterns or payloads to mbDIALUP service port
- Outbound connections from mbDIALUP system to suspicious IPs
SIEM Query:
source="mbDIALUP" AND (event_type="http_request" AND (uri="*crafted*" OR user_agent="*unusual*")) OR (process_name="mbDIALUP" AND child_process!="expected_process")