CVE-2021-28799 (GCVE-0-2021-28799)
Vulnerability from cvelistv5 – Published: 2021-05-13 02:55 – Updated: 2025-10-21 23:25Title
Improper Authorization Vulnerability in HBS 3 (Hybrid Backup Sync)
Summary
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 .
Severity
10 (Critical)
SSVC
Exploitation: active
Automatable: yes
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2025-02-04 14:53 UTC
CWE
- CWE-285 - Improper Authorization
Assigner
References
2 references
| URL | Tags |
|---|---|
| https://www.qnap.com/en/security-advisory/QSA-21-13 | x_refsource_MISC |
| https://www.cisa.gov/known-exploited-vulnerabilit… | government-resource |
Impacted products
6 products
| Vendor | Product | Version | |
|---|---|---|---|
| QNAP Systems Inc. | HBS 3 |
Affected:
unspecified , < v16.0.0415
(custom)
|
|
| QNAP Systems Inc. | HBS 3 |
Affected:
unspecified , < v3.0.210412
(custom)
|
|
| QNAP Systems Inc. | HBS 3 |
Affected:
unspecified , < v3.0.210411
(custom)
|
|
| QNAP Systems Inc. | HBS 3 |
Affected:
unspecified , < v16.0.0419
(custom)
|
|
| QNAP Systems Inc. | HBS 2 |
Unaffected:
all versions
|
|
| QNAP Systems Inc. | HBS 1.3 |
Unaffected:
all versions
|
Date Public
2021-04-22 00:00
CISA
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: c25e48cf-ba07-4eac-8875-da308508bdf2
Exploited: Yes
Timestamps
First Seen: 2022-03-31
Asserted: 2022-03-31
Scope
Notes: QNAP NAS Improper Authorization Vulnerability | Affected: QNAP / Network Attached Storage (NAS) | Description: QNAP NAS running HBS 3 contains an improper authorization vulnerability which can allow remote attackers to log in to a device. | Required action: Apply updates per vendor instructions. | Due date: 2022-04-21 | Known ransomware campaign use (KEV): Known | Notes (KEV): https://nvd.nist.gov/vuln/detail/CVE-2021-28799
Evidence
Type: Vendor Report
Signal: Successful Exploitation
Confidence: 80%
Source: cisa-kev
Details
| Cwes | CWE-285 |
|---|---|
| Feed | CISA Known Exploited Vulnerabilities Catalog |
| Product | Network Attached Storage (NAS) |
| Due Date | 2022-04-21 |
| Date Added | 2022-03-31 |
| Vendorproject | QNAP |
| Vulnerabilityname | QNAP NAS Improper Authorization Vulnerability |
| Knownransomwarecampaignuse | Known |
References
Created: 2026-10-02 08:10 CEST
| Updated: 2026-10-02 08:10 CEST
Previdian
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: 3ed4f544-7e85-4e9a-b684-fc4cf7759721
Exploited: Yes
Timestamps
First Seen: 2022-03-31
Asserted: 2022-03-31
Scope
Notes: Improper Authorization Vulnerability in HBS 3 (Hybrid Backup Sync) | Affected: QNAP / HBS 3, HBS 2, HBS 1.3 | CVSS: 10.0 (CRITICAL) | EPSS: 0.7825 | Used in malware: yes | Not yet in CISA KEV: False
Evidence
Type: Public Report
Signal: Confirmed Compromise
Confidence: 70%
Source: previdian
Details
| Feed | Previdian (previdian.com) |
|---|---|
| Title | Improper Authorization Vulnerability in HBS 3 (Hybrid Backup Sync) |
| Cve Id | CVE-2021-28799 |
| Vendor | QNAP |
| Ghsa Id | None |
| Product | HBS 3, HBS 2, HBS 1.3 |
| Added Date | 2022-03-31T00:00:00.000Z |
| Cvss Score | 10.0 |
| Epss Score | 0.7825 |
| Previous Ids | |
| Cvss Severity | CRITICAL |
| Virtual Patch | False |
| Cvss Estimated | False |
| Epss Percentile | 0.99567 |
| Used In Malware | yes |
| Vulnerability Id | CVE-2021-28799 |
| Ahead Of Cisa Kev | None |
| Not Yet In Cisa Kev | False |
References
Created: 2026-10-02 09:11 CEST
| Updated: 2026-10-02 09:11 CEST
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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