CVE-2024-20687
📋 TL;DR
This vulnerability in Microsoft's AllJoyn API allows attackers to cause a denial of service by sending specially crafted packets. It affects systems running Windows with AllJoyn enabled, potentially causing service crashes or system instability. The vulnerability requires network access to the affected system.
💻 Affected Systems
- Microsoft Windows
📦 What is this software?
Windows 10 1507 by Microsoft
Windows 10 1507 by Microsoft
Windows 10 1607 by Microsoft
Windows 10 1607 by Microsoft
Windows 10 1809 by Microsoft
Windows 10 21h2 by Microsoft
Windows 10 22h2 by Microsoft
Windows 11 21h2 by Microsoft
Windows 11 21h2 by Microsoft
Windows 11 22h2 by Microsoft
Windows 11 22h2 by Microsoft
Windows 11 23h2 by Microsoft
Windows 11 23h2 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Complete system crash or persistent denial of service requiring reboot, potentially affecting multiple services that depend on AllJoyn functionality.
Likely Case
Temporary service disruption or application crashes affecting AllJoyn-dependent functionality until system restart.
If Mitigated
Minimal impact with proper network segmentation and access controls limiting exposure to trusted networks only.
🎯 Exploit Status
Exploitation requires network access to the vulnerable system but no authentication. The CWE-125 (Out-of-bounds Read) suggests memory corruption that could lead to crashes.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: January 2024 security updates (KB5034123 for Windows 10, KB5034127 for Windows 11, etc.)
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2024-20687
Restart Required: Yes
Instructions:
1. Install the January 2024 Windows security updates via Windows Update. 2. Alternatively, download and install the specific KB update for your Windows version from Microsoft Update Catalog. 3. Restart the system after installation.
🔧 Temporary Workarounds
Disable AllJoyn Service
windowsDisable the AllJoyn Router Service if not required for your environment
sc stop AJRouter
sc config AJRouter start= disabled
Block AllJoyn Network Ports
windowsBlock network access to AllJoyn ports (typically 9955-9956 TCP/UDP) using firewall rules
netsh advfirewall firewall add rule name="Block AllJoyn" dir=in action=block protocol=TCP localport=9955-9956
netsh advfirewall firewall add rule name="Block AllJoyn UDP" dir=in action=block protocol=UDP localport=9955-9956
🧯 If You Can't Patch
- Implement strict network segmentation to isolate systems with AllJoyn enabled from untrusted networks
- Monitor for unusual network traffic to AllJoyn ports (9955-9956) and system crashes related to AllJoyn services
🔍 How to Verify
Check if Vulnerable:
Check if AllJoyn Router Service (AJRouter) is running and if system has January 2024 security updates installedCheck Version:
wmic qfe list | findstr KB5034123 (or appropriate KB for your Windows version)Verify Fix Applied:
Verify January 2024 security updates are installed and AllJoyn service is either updated or disabled📡 Detection & Monitoring
Log Indicators:
- Event ID 1000 or 1001 application crashes for AllJoyn processes
- System event logs showing service crashes for AJRouter
Network Indicators:
- Unusual traffic to TCP/UDP ports 9955-9956
- Multiple connection attempts to AllJoyn services
SIEM Query:
EventID=1000 AND ProcessName="AJRouter.exe" OR EventID=7034 AND ServiceName="AJRouter"