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

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 .

10.0 CRITICALEPSS 78.25%⚡ Known Exploited (CISA KEV)NVD: Analyzed

Last updated: 2026-06-17 03:46 UTC

OverviewCVSS details

10.0CRITICALCVSS 3.1

Score source: qnap (CNA)
NVD status: Analyzed
Published: May 13, 2021
Assigner: qnap

Affected

HBS 3 (QNAP Systems Inc.)

Versions: before v16.0.0415
Fixed in: v16.0.0415

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Exploitation

Public exploit: None listed
CISA KEV: Listed · Mar 31, 2022
KEV due date: Apr 21, 2022
Ransomware use: Known
SSVC: Exploitation active · Automatable yes · Impact total

EPSS · FIRST, scored Nov 7

78.25%chance of exploitation in 30 days

Higher than 99.58% of CVEs

CVSS 3.1 · qnap (CNA)

10.0Critical

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

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Changed
Confidentiality impact: High
Integrity impact: High
Availability impact: High

CVSS 3.1 · NVD

9.8Critical

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

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: High
Integrity impact: High
Availability impact: High

CVSS 2.0 · NVD

7.5High

AV:N/AC:L/Au:N/C:P/I:P/A:P

Attack vector: Network
Attack complexity: Low
Authentication: None
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Partial

NVD status: Analyzed

Overview Affected Products References

NVD CVE.org

Overview

Severity

Score	Severity	Version	Vector String
10.0	CRITICAL	3.1qnap (CNA)	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
9.8	CRITICAL	3.1NVD	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5	HIGH	2.0NVD	AV:N/AC:L/Au:N/C:P/I:P/A:P

CISA required action

⚡ Known exploited · remediation due Apr 21, 2022

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Details

CVE ID: CVE-2021-28799
Status: Analyzed
Assigner (CNA): qnap
Published: May 13, 2021
Last modified: 2026-06-17 03:46 UTC
Weaknesses: CWE-285 · Improper Authorization

Sources

Refreshed hourly from the sources above. Last fetched 2026-11-08 13:26 UTC.