CVE-2021-28799 CRITICAL

CVE-2021-28799: Improper Authorization Vulnerability in HBS 3 (Hybrid Backup Sync)

Vendor Qnap Systems Inc.
Product HBS 3
Weakness CWE-285
KEV Status Known Exploited
Ransomware Used in campaigns
Published May 13, 2021
Last update October 21, 2025
View on NVD All CVEs

CVSS base score

10.0/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality High
Integrity High

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

What the vulnerability does

01Description

An improper authorization vulnerability has been reported to affect QNAP NAS running HBS 3 (Hybrid Backup Sync. ) If exploited, the vulnerability allows remote attackers to log in to a device. This issue affects: QNAP Systems Inc. HBS 3 versions prior to v16.0.0415 on QTS 4.5.2; versions prior to v3.0.210412 on QTS 4.3.6; versions prior to v3.0.210411 on QTS 4.3.4; versions prior to v3.0.210411 on QTS 4.3.3; versions prior to v16.0.0419 on QuTS hero h4.5.1; versions prior to v16.0.0419 on QuTScloud c4.5.1~c4.5.4. This issue does not affect: QNAP Systems Inc. HBS 2 . QNAP Systems Inc. HBS 1.3 .

CISA mandated remediation

02CISA Required Action

Apply updates per vendor instructions.

Key dates

03Disclosure timeline

May 13, 2021 CVE published
October 21, 2025 Record updated

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