CVE-2021-28809: QNAP Hybrid Backup Sync

Critical severity, CVSS 9.8. EPSS: 16.1% chance of exploitation in the next 30 days.

An improper access control vulnerability has been reported to affect certain legacy versions of HBS 3. If exploited, this vulnerability allows attackers to compromise the security of the operating system.QNAP have already fixed this vulnerability in the following versions of HBS 3: QTS 4.3.6: HBS 3 v3.0.210507 and later QTS 4.3.4: HBS 3 v3.0.210506 and later QTS 4.3.3: HBS 3 v3.0.210506 and later

Affected products

• QNAP Hybrid Backup Sync: before 3.0.210507 (fixed in 3.0.210507); before 3.0.210506 (fixed in 3.0.210506)

Published 2021-07-08. Last modified 2026-06-17.