CVE-2021-33183
📋 TL;DR
This path traversal vulnerability in Synology Docker's container volume management allows local users to bypass directory restrictions and access arbitrary files on the host system. It affects Synology NAS devices running vulnerable versions of Docker Package, requiring local access to exploit.
💻 Affected Systems
- Synology Docker Package
📦 What is this software?
Docker by Synology
⚠️ Risk & Real-World Impact
Worst Case
Local attackers could read sensitive system files, write malicious files to critical locations, or potentially escalate privileges to gain full control of the NAS device.
Likely Case
Malicious local users or compromised containers could access sensitive data from other containers or the host system, potentially stealing credentials or configuration files.
If Mitigated
With proper access controls and container isolation, impact would be limited to the compromised container's scope.
🎯 Exploit Status
Exploitation requires local access but vectors are unspecified in advisory. Likely involves manipulating volume mount paths.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 18.09.0-0515 and later
Vendor Advisory: https://www.synology.com/security/advisory/Synology_SA_21_08
Restart Required: Yes
Instructions:
1. Log into DSM web interface. 2. Open Package Center. 3. Find Docker Package. 4. Click Update if available. 5. Alternatively, uninstall and reinstall latest version. 6. Restart Docker service or reboot NAS.
🔧 Temporary Workarounds
Restrict Docker Access
allLimit which users can access Docker and run containers to trusted administrators only.
Container Isolation
linuxRun containers with minimal privileges and avoid mounting sensitive host directories.
docker run --read-only --security-opt=no-new-privileges image_name
🧯 If You Can't Patch
- Remove Docker Package entirely if not needed
- Implement strict access controls and audit all container configurations
🔍 How to Verify
Check if Vulnerable:
Check Docker Package version in DSM Package Center or run: cat /var/packages/Docker/etc/package_info | grep versionCheck Version:
cat /var/packages/Docker/etc/package_info | grep versionVerify Fix Applied:
Verify Docker Package version is 18.09.0-0515 or later in Package Center📡 Detection & Monitoring
Log Indicators:
- Unusual file access patterns from Docker containers
- Path traversal attempts in container logs
- Access to sensitive host paths from container processes
Network Indicators:
- Not applicable - local vulnerability
SIEM Query:
source="docker" AND (path="../../" OR path="../" OR "path traversal")