CVE-2021-26560
📋 TL;DR
CVE-2021-26560 allows man-in-the-middle attackers to intercept and spoof servers during HTTP sessions with synoagentregisterd in Synology DSM. This cleartext transmission vulnerability affects Synology DiskStation Manager users before version 6.2.3-25426-3.
💻 Affected Systems
- Synology DiskStation Manager
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers could intercept sensitive information, spoof legitimate servers, and potentially gain unauthorized access to the DiskStation management system.
Likely Case
Information disclosure and server spoofing in environments where attackers can intercept network traffic between clients and the DiskStation.
If Mitigated
Limited impact with proper network segmentation, TLS enforcement, and updated systems.
🎯 Exploit Status
Exploitation requires man-in-the-middle position in network path.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: DSM 6.2.3-25426-3 and later
Vendor Advisory: https://www.synology.com/security/advisory/Synology_SA_20_26
Restart Required: Yes
Instructions:
1. Log into DSM web interface. 2. Navigate to Control Panel > Update & Restore. 3. Click 'Download' for available updates. 4. Click 'Install' when download completes. 5. System will restart automatically.
🔧 Temporary Workarounds
Network Segmentation
allIsolate DiskStation from untrusted networks and limit access to trusted IPs only.
VPN Enforcement
allRequire VPN for all remote access to DiskStation management interface.
🧯 If You Can't Patch
- Implement strict network access controls to limit exposure
- Monitor for unusual network traffic patterns and authentication attempts
🔍 How to Verify
Check if Vulnerable:
Check DSM version in Control Panel > Info Center > DSM version. If version is below 6.2.3-25426-3, system is vulnerable.Check Version:
ssh admin@diskstation 'cat /etc.defaults/VERSION'Verify Fix Applied:
Verify DSM version is 6.2.3-25426-3 or higher after update.📡 Detection & Monitoring
Log Indicators:
- Unusual authentication patterns
- Multiple failed registration attempts
- Unexpected source IPs accessing synoagentregisterd
Network Indicators:
- Cleartext HTTP traffic to DiskStation on registration ports
- Unencrypted agent registration communications
SIEM Query:
source="synology" AND (event="authentication_failure" OR event="registration_failure")