CVE-2020-27654
📋 TL;DR
CVE-2020-27654 is an improper access control vulnerability in the lbd service of Synology Router Manager (SRM) that allows remote attackers to execute arbitrary commands without authentication. Attackers can exploit this by sending specially crafted requests to TCP ports 7786 or 7787. This affects Synology router users running vulnerable SRM versions.
💻 Affected Systems
- Synology Router Manager (SRM)
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the router with root-level command execution, allowing attackers to intercept network traffic, deploy malware, pivot to internal networks, and maintain persistent access.
Likely Case
Remote code execution leading to router takeover, network traffic monitoring, DNS hijacking, and credential theft from connected devices.
If Mitigated
No impact if patched or if vulnerable ports are blocked by network controls.
🎯 Exploit Status
Exploitation is straightforward - attackers send crafted requests to the vulnerable ports. Multiple public PoCs and detailed technical analysis are available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: SRM 1.2.4-8081 and later
Vendor Advisory: https://www.synology.com/security/advisory/Synology_SA_20_14
Restart Required: Yes
Instructions:
1. Log into Synology Router Manager web interface. 2. Navigate to Control Panel > Update & Restore. 3. Check for updates and install SRM 1.2.4-8081 or later. 4. Reboot the router after installation.
🔧 Temporary Workarounds
Block vulnerable ports with firewall
linuxBlock inbound and outbound traffic to TCP ports 7786 and 7787 on the router
iptables -A INPUT -p tcp --dport 7786 -j DROP
iptables -A INPUT -p tcp --dport 7787 -j DROP
iptables -A OUTPUT -p tcp --dport 7786 -j DROP
iptables -A OUTPUT -p tcp --dport 7787 -j DROP
Disable remote management
allEnsure router management interface is not exposed to the internet
🧯 If You Can't Patch
- Isolate vulnerable routers in a separate network segment with strict access controls
- Implement network monitoring for traffic to/from ports 7786 and 7787
🔍 How to Verify
Check if Vulnerable:
Check SRM version in web interface: Control Panel > Info Center > DSM/SRM Version. If version is earlier than 1.2.4-8081, system is vulnerable.Check Version:
ssh admin@[router_ip] 'cat /etc.defaults/VERSION' | grep majorversionVerify Fix Applied:
Verify SRM version is 1.2.4-8081 or later. Test if ports 7786 and 7787 are still accessible: 'nc -zv [router_ip] 7786 7787' should show connection refused.📡 Detection & Monitoring
Log Indicators:
- Unusual connections to ports 7786/7787 in router logs
- Failed authentication attempts followed by successful lbd service access
- Unexpected process execution or configuration changes
Network Indicators:
- Traffic to TCP ports 7786 or 7787 from unexpected sources
- Large or unusual payloads sent to these ports
- Outbound connections from router to suspicious IPs post-exploitation
SIEM Query:
source="synology-router" (dest_port=7786 OR dest_port=7787) AND (payload_size>1000 OR protocol_violation=true)🔗 References
- https://www.synology.com/security/advisory/Synology_SA_20_14
- https://www.talosintelligence.com/vulnerability_reports/TALOS-2020-1064
- https://www.talosintelligence.com/vulnerability_reports/TALOS-2020-1065
- https://www.synology.com/security/advisory/Synology_SA_20_14
- https://www.talosintelligence.com/vulnerability_reports/TALOS-2020-1064
- https://www.talosintelligence.com/vulnerability_reports/TALOS-2020-1065
