CVE-2021-28798
📋 TL;DR
This CVE describes a relative path traversal vulnerability in QNAP NAS devices running QTS and QuTS hero operating systems. If exploited, attackers can modify system files, potentially compromising system integrity. Affected users are those running vulnerable versions of QNAP NAS software.
💻 Affected Systems
- QNAP NAS running QTS
- QNAP NAS running QuTS hero
📦 What is this software?
Qts by Qnap
Qts by Qnap
Qts by Qnap
⚠️ Risk & Real-World Impact
Worst Case
Attackers could modify critical system files, install persistent malware, gain full system control, or render the NAS inoperable.
Likely Case
Attackers modify configuration files to gain unauthorized access, escalate privileges, or disrupt NAS services.
If Mitigated
With proper network segmentation and access controls, impact is limited to the NAS device itself without lateral movement.
🎯 Exploit Status
Requires some level of access to the NAS, but path traversal vulnerabilities are commonly exploited once discovered.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: QTS 4.5.2.1630 Build 20210406 or later, QTS 4.3.6.1663 Build 20210504 or later, QTS 4.3.3.1624 Build 20210416 or later, QuTS hero h4.5.2.1638 Build 20210414 or later
Vendor Advisory: https://www.qnap.com/zh-tw/security-advisory/qsa-21-14
Restart Required: Yes
Instructions:
1. Log into QNAP NAS web interface. 2. Go to Control Panel > System > Firmware Update. 3. Check for updates and install the latest firmware. 4. Reboot the NAS after update completes.
🔧 Temporary Workarounds
Network Segmentation
allIsolate QNAP NAS from internet and restrict access to trusted networks only
Access Control Restrictions
allLimit user permissions and disable unnecessary services on the NAS
🧯 If You Can't Patch
- Disable all internet-facing services and ports on the NAS
- Implement strict network firewall rules to limit access to the NAS
🔍 How to Verify
Check if Vulnerable:
Check QTS/QuTS hero version in Control Panel > System > Firmware UpdateCheck Version:
ssh admin@nas_ip 'cat /etc/config/uLinux.conf | grep version'Verify Fix Applied:
Verify firmware version matches or exceeds the patched versions listed in the advisory📡 Detection & Monitoring
Log Indicators:
- Unusual file modification patterns in system logs
- Failed path traversal attempts in web server logs
Network Indicators:
- Unusual outbound connections from NAS
- Unexpected file transfer patterns
SIEM Query:
source="qnap_nas" AND (event_type="file_modification" OR path="../")