CVE-2021-27648
📋 TL;DR
This vulnerability in Synology Antivirus Essential allows remote authenticated users to escalate privileges by exploiting an externally controlled reference to a resource in another sphere in the quarantine functionality. Attackers with valid credentials can gain elevated system privileges. Only affects Synology Antivirus Essential users running vulnerable versions.
💻 Affected Systems
- Synology Antivirus Essential
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise where authenticated attackers gain root/administrator privileges, potentially leading to data theft, ransomware deployment, or persistent backdoor installation.
Likely Case
Privilege escalation allowing attackers to bypass security controls, access sensitive data, or install malicious software on affected systems.
If Mitigated
Limited impact if proper network segmentation, least privilege access, and monitoring are in place, though privilege escalation would still be possible for authenticated users.
🎯 Exploit Status
Exploitation requires authenticated access and knowledge of unspecified vectors. No public exploit code available at time of advisory.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.4.8-2801
Vendor Advisory: https://www.synology.com/security/advisory/Synology_SA_21_15
Restart Required: Yes
Instructions:
1. Log into DSM as administrator. 2. Open Package Center. 3. Find Synology Antivirus Essential. 4. Click Update if available. 5. Alternatively, uninstall and reinstall latest version. 6. Restart the system after update.
🔧 Temporary Workarounds
Disable Antivirus Essential
allTemporarily disable Synology Antivirus Essential until patching is possible
Open Package Center > Select Synology Antivirus Essential > Click Stop
Restrict Access
allLimit access to DSM management interface to trusted IPs only
Control Panel > Security > Firewall > Create rules to restrict DSM access
🧯 If You Can't Patch
- Remove Synology Antivirus Essential package entirely
- Implement strict access controls and monitor for privilege escalation attempts
🔍 How to Verify
Check if Vulnerable:
Check Package Center for Synology Antivirus Essential version. If version is below 1.4.8-2801, system is vulnerable.Check Version:
ssh admin@synology_ip 'synopkg version AntivirusEssential'Verify Fix Applied:
Verify Synology Antivirus Essential version shows 1.4.8-2801 or higher in Package Center.📡 Detection & Monitoring
Log Indicators:
- Unusual privilege escalation events in system logs
- Multiple failed authentication attempts followed by successful login
- Unexpected process execution with elevated privileges
Network Indicators:
- Unusual outbound connections from DSM system
- Traffic patterns suggesting lateral movement
SIEM Query:
source="synology" AND (event_type="privilege_escalation" OR process_name="antivirus" AND action="execute")