---
title: "CVE-2021-28799: Improper Authorization Vulnerability… | CubePath"
description: "An improper authorization vulnerability has been reported to affect QNAP NAS running HBS 3 (Hybrid Backup Sync. ) If exploited, the vulnerability…"
language: en
source: https://cubepath.com/security/cve/CVE-2021-28799
---

# CVE-2021-28799: Improper Authorization Vulnerability… | CubePath

## Description

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 .

Official description from the CVE record, published by qnap. Copyright © 1999-2026 The MITRE Corporation. See [/security/cve/legal](https://cubepath.com/security/cve/legal) for the CVE license. [View the record on cve.org](https://www.cve.org/CVERecord?id=CVE-2021-28799)

## Key data

### CVSS 3.1 Critical 10.0

Score published by qnap in the CVE record.

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

| Metric                 | Value   | What it means                                                                       |
| ---------------------- | ------- | ----------------------------------------------------------------------------------- |
| Attack vector          | Network | The vulnerable component can be reached over a network, possibly from the Internet. |
| Attack complexity      | Low     | No special conditions are needed. The attack can be repeated at will.               |
| Privileges required    | None    | No account or privileges are needed.                                                |
| User interaction       | None    | No action from any user is needed.                                                  |
| Scope                  | Changed | The impact can reach other components beyond the vulnerable one.                    |
| Confidentiality impact | High    | Serious or total effect on the secrecy of data.                                     |
| Integrity impact       | High    | Serious or total effect on the trustworthiness of data.                             |
| Availability impact    | High    | Serious or total effect on availability.                                            |

CVSS is owned and managed by FIRST.Org, Inc. (FIRST) and is used by permission. Each CVSS score on this site is shown together with its vector string, as published in the CVE record by the source named next to it. Learn more at [first.org/cvss](https://www.first.org/cvss/) .

### EPSS

Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days.

Score

0.78250 (78.3% probability)

Percentile

99.6%

Scores of

Nov 10, 2026

Model

v2026.06.15

### CISA Known Exploited Vulnerabilities

This CVE is listed in the CISA KEV catalog.

Name in the catalog

QNAP NAS Improper Authorization Vulnerability

Added to the catalog

Mar 31, 2022

Federal due date

Apr 21, 2022

Ransomware campaigns

Known use

### CISA assessment as of Feb 4, 2025

Stakeholder-Specific Vulnerability Categorization (SSVC) decision points added by CISA.

Exploitation

Recorded by CISA as active

Automatable

yes

Technical impact

total

### Weakness (CWE)

CWE catalog version 5.0.

CWE names: Copyright © 2006-2026, The MITRE Corporation. See [/security/cve/legal](https://cubepath.com/security/cve/legal) for the CWE license.

- [CWE-285](https://cwe.mitre.org/data/definitions/285.html) Improper Authorization

## Affected products

Products listed in the CVE record, as the CNA published them.

- QNAP Systems Inc. HBS 3

  - affected: unspecified up to before v16.0.0415
- QNAP Systems Inc. HBS 3

  - affected: unspecified up to before v3.0.210412
- QNAP Systems Inc. HBS 3

  - affected: unspecified up to before v3.0.210411
- QNAP Systems Inc. HBS 3

  - affected: unspecified up to before v3.0.210411
- QNAP Systems Inc. HBS 3

  - affected: unspecified up to before v16.0.0419
- QNAP Systems Inc. HBS 3

  - affected: unspecified up to before v16.0.0419
- QNAP Systems Inc. HBS 2

  - unaffected: all versions
- QNAP Systems Inc. HBS 1.3

  - unaffected: all versions

## References

Links listed in the CVE record. They lead to other sites, which CubePath does not control.

- [qnap.com/en/security-advisory/QSA-21-13](https://www.qnap.com/en/security-advisory/QSA-21-13)

## Timeline

1. ID reserved Mar 18, 2021
2. Record published May 13, 2021
3. Added to CISA KEV Mar 31, 2022
4. Record last updated Oct 21, 2025

## Look up another CVE

## About CubePath

CubePath is a cloud provider with data centers in Europe and the United States. It offers VPS, bare metal servers and DDoS protection.

[Cloud VPS](https://cubepath.com/vps) [DDoS protection](https://cubepath.com/ddos-protection)

Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 19:29 UTC. [Sources and licenses](https://cubepath.com/security/cve/legal)