CVE-2022-33633
📋 TL;DR
CVE-2022-33633 is a remote code execution vulnerability in Skype for Business and Lync that allows an attacker to execute arbitrary code on affected systems. Attackers can exploit this vulnerability by sending specially crafted requests to vulnerable servers. Organizations running Skype for Business or Lync servers are affected.
💻 Affected Systems
- Skype for Business Server
- Lync Server
📦 What is this software?
Lync Server by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise allowing attacker to install programs, view/change/delete data, or create new accounts with full user rights on the affected server.
Likely Case
Attacker gains control of the Skype for Business/Lync server, potentially accessing sensitive communications data and using the server as a foothold for lateral movement.
If Mitigated
With proper network segmentation and access controls, impact limited to the isolated server environment.
🎯 Exploit Status
Microsoft has rated this as 'Exploitation More Likely' in their security advisory. The vulnerability requires no authentication to exploit.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: July 2022 security updates
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2022-33633
Restart Required: Yes
Instructions:
1. Download the July 2022 security updates for Skype for Business Server or Lync Server from Microsoft Update Catalog. 2. Apply the updates to all affected servers. 3. Restart the servers as required.
🔧 Temporary Workarounds
Block external access
allRestrict network access to Skype for Business/Lync servers to trusted internal networks only
Use firewall rules to block inbound traffic to ports 5061, 444, 443 from untrusted networks
Network segmentation
allIsolate Skype for Business/Lync servers in a separate network segment
🧯 If You Can't Patch
- Immediately isolate affected servers from internet access and restrict to internal trusted networks only
- Implement strict network monitoring and anomaly detection for traffic to Skype for Business/Lync servers
🔍 How to Verify
Check if Vulnerable:
Check if Skype for Business Server or Lync Server is installed and if July 2022 security updates are not appliedCheck Version:
Get-WmiObject -Class Win32_Product | Where-Object {$_.Name -like '*Skype for Business*' -or $_.Name -like '*Lync*'} | Select-Object Name, VersionVerify Fix Applied:
Verify that July 2022 security updates are installed and server version shows updated build numbers📡 Detection & Monitoring
Log Indicators:
- Unusual authentication failures
- Abnormal process creation on Skype for Business servers
- Suspicious PowerShell or command execution
Network Indicators:
- Unusual traffic patterns to Skype for Business/Lync ports (5061, 444, 443)
- Malformed requests to Skype for Business services
SIEM Query:
source="SkypeForBusiness" AND (event_id=300 OR event_id=301) AND (process_name="powershell.exe" OR process_name="cmd.exe")