CVE-2021-29085
📋 TL;DR
This vulnerability allows remote attackers to read arbitrary files on Synology DiskStation Manager (DSM) systems through improper input sanitization in the file sharing management component. Attackers can exploit this injection flaw without authentication to access sensitive system files. All DSM users with affected versions are at risk.
💻 Affected Systems
- Synology DiskStation Manager (DSM)
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise through reading of configuration files, credentials, or sensitive data leading to privilege escalation and lateral movement.
Likely Case
Unauthorized access to sensitive files including configuration data, user information, and potentially credentials stored on the system.
If Mitigated
Limited impact with proper network segmentation and access controls preventing external exploitation attempts.
🎯 Exploit Status
The advisory mentions remote attackers can exploit this via unspecified vectors, suggesting relatively straightforward exploitation once vectors are identified.
🛠️ 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 as administrator. 2. Navigate to Control Panel > Update & Restore. 3. Click 'Update DSM' and follow prompts to install version 6.2.3-25426-3 or later. 4. System will restart automatically after update.
🔧 Temporary Workarounds
Disable File Sharing Services
allTemporarily disable file sharing services to prevent exploitation while awaiting patch
Network Segmentation
allRestrict access to DSM management interface to trusted networks only
🧯 If You Can't Patch
- Implement strict network access controls to limit DSM management interface exposure
- Enable comprehensive logging and monitoring for file access anomalies
🔍 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@nas_ip 'cat /etc.defaults/VERSION' | grep productversionVerify Fix Applied:
After updating, verify DSM version shows 6.2.3-25426-3 or higher in Control Panel > Info Center.📡 Detection & Monitoring
Log Indicators:
- Unusual file access patterns in DSM logs
- Multiple failed file access attempts from single source
- Access to sensitive system files from unprivileged users
Network Indicators:
- HTTP requests to file sharing endpoints with unusual parameters
- Traffic spikes to DSM management interface
SIEM Query:
source="dsm_logs" AND (event_type="file_access" AND (file_path="/etc/*" OR file_path="/var/*")) AND user!="admin"