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CVE-2021-44596

9.8 CRITICAL
Remote Code Execution

📋 TL;DR

This vulnerability allows unauthenticated remote attackers to execute arbitrary code with SYSTEM privileges on affected Wondershare Dr. Fone installations. Attackers can exploit UDP communication with the InstallAssistService.exe service to run malicious executables without validation. All users running vulnerable versions are affected.

💻 Affected Systems

Products:
  • Wondershare Dr. Fone
Versions: Versions up to and including 2021-12-06
Operating Systems: Windows
Default Config Vulnerable: ⚠️ Yes
Notes: InstallAssistService.exe runs with SYSTEM privileges by default, making exploitation particularly dangerous.

📦 What is this software?

Dr.fone by Wondershare

View all CVEs affecting Dr.fone →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete system compromise with SYSTEM privileges, enabling installation of persistent malware, data theft, and lateral movement across networks.

🟠

Likely Case

Remote code execution leading to ransomware deployment, credential harvesting, or backdoor installation on vulnerable systems.

🟢

If Mitigated

Limited impact if proper network segmentation and endpoint protection block UDP exploitation attempts.

🌐 Internet-Facing: HIGH - Unauthenticated remote exploitation via UDP makes internet-facing systems extremely vulnerable.
🏢 Internal Only: HIGH - Even internally, unauthenticated exploitation allows lateral movement and privilege escalation.

🎯 Exploit Status

Public PoC: ⚠️ Yes
Weaponized: CONFIRMED
Unauthenticated Exploit: ⚠️ Yes
Complexity: LOW

Public exploit code exists in Packet Storm and other sources, making this easily weaponizable.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Version after 2021-12-06

Vendor Advisory: http://wondershare.com

Restart Required: Yes

Instructions:

1. Update Wondershare Dr. Fone to latest version. 2. Restart the system. 3. Verify InstallAssistService.exe is no longer vulnerable.

🔧 Temporary Workarounds

Block UDP Communication

windows

Block UDP traffic to InstallAssistService.exe using Windows Firewall

New-NetFirewallRule -DisplayName "Block DrFone UDP" -Direction Inbound -Protocol UDP -Program "C:\Program Files\Wondershare\Dr.Fone\InstallAssistService.exe" -Action Block

Disable Service

windows

Stop and disable the vulnerable InstallAssistService

sc stop InstallAssistService
sc config InstallAssistService start= disabled

🧯 If You Can't Patch

  • Segment network to restrict UDP traffic to affected systems
  • Implement strict endpoint detection and response (EDR) to monitor for suspicious process execution

🔍 How to Verify

Check if Vulnerable:

Check if InstallAssistService.exe is running and listening on UDP ports, and verify Dr. Fone version is 2021-12-06 or earlier.

Check Version:

Check Dr. Fone 'About' section in application or examine installation directory version information.

Verify Fix Applied:

Confirm Dr. Fone version is newer than 2021-12-06 and InstallAssistService.exe no longer accepts unauthenticated UDP commands.

📡 Detection & Monitoring

Log Indicators:

  • UDP connections to InstallAssistService.exe from unexpected sources
  • Suspicious child processes spawned by InstallAssistService.exe

Network Indicators:

  • UDP traffic to port used by InstallAssistService.exe (typically high random port)
  • Unusual outbound connections following UDP communication

SIEM Query:

Process Creation where Parent Process Name contains 'InstallAssistService.exe' AND Command Line contains suspicious executables

📊 Metadata

CVE ID: CVE-2021-44596
CVSS v3 Score: 9.8 (CRITICAL)
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published: April 29, 2022
Last Updated: November 21, 2024

🔗 References

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