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ExploitedIn CISA KEVFix available

CVE-2021-28799

Exploitation confirmed. First attested on 2022-03-31 by CISA-ADP, CISA KEV, GCVE · kevintel, GCVE · shadowserver.

  • Published2021-05-13
  • Fixed in16.0.0419 · 16.0.0415 · 3.0.210412 · 3.0.210411
  • WeaknessCWE-285

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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 .

Timeline

dates in UTC
  1. 2021-05-1303:15CVE publishedNVD
  2. 2022-03-31Added to the CISA KEV catalogCISA KEV
  3. 2022-03-31Listed as exploited by GCVEGCVE
  4. 2022-03-31Exploitation first reportedCISA KEV
  5. 2025-02-0414:53SSVC exploitation set to activeCISA-ADP

Observed activity

isMalicious corpus · updated 2026-11-03 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-28799?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-28799?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Qnap hybrid backup syncversion to verify
BranchAffectedFixed in
16.0< 16.0.041916.0.0419
16.0< 16.0.041516.0.0415
3.0< 3.0.2104123.0.210412
3.0< 3.0.2104113.0.210411

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Products declared by the CNA8 products

As qnap, the CNA that assigned this CVE, declared them in the CVE record; versions as written.

  • QNAP Systems Inc. HBS 3

    platforms: QTS 4.5.2

    Affected
    • < v16.0.0415fixed in v16.0.0415custom
  • QNAP Systems Inc. HBS 3

    platforms: QTS 4.3.6

    Affected
    • < v3.0.210412fixed in v3.0.210412custom
  • QNAP Systems Inc. HBS 3

    platforms: QTS 4.3.4

    Affected
    • < v3.0.210411fixed in v3.0.210411custom
  • QNAP Systems Inc. HBS 3

    platforms: QTS 4.3.3

    Affected
    • < v3.0.210411fixed in v3.0.210411custom
  • QNAP Systems Inc. HBS 3

    platforms: QuTS hero h4.5.1

    Affected
    • < v16.0.0419fixed in v16.0.0419custom
  • QNAP Systems Inc. HBS 3

    platforms: QuTScloud c4.5.1~c4.5.4

    Affected
    • < v16.0.0419fixed in v16.0.0419custom

2 more products in the CVE record.

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2021-05-13

Fix

  1. Update Qnap hybrid backup sync to 16.0.0419 · 16.0.0415 · 3.0.210412 · 3.0.210411
  2. CISA’s required action: Apply updates per vendor instructions.due 2022-04-21

Advisories and patches

Detection

read 2026-11-02 22:42 UTC
Nuclei template
available
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub
Metasploit modules
none listed
Metasploit Framework

CISA Known Exploited Vulnerability

Date Added
2022-03-31
Patch Due Date
2022-04-21
Ransomware Use
Known
Required Action
Apply updates per vendor instructions.

Sources

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published
2021-05-13
Last Modified
2026-06-17
NVD status
Analyzed
GitHub Advisory
GHSA-4v9x-j7pr-8wxq

Frequently asked questions

What is CVE-2021-28799?

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 .

Is CVE-2021-28799 actively exploited?

Yes. CVE-2021-28799 is on the CISA Known Exploited Vulnerabilities (KEV) catalog, meaning it has been confirmed as actively exploited in the wild. CISA requires federal agencies to patch by 2022-04-21.

What is the CVSS score for CVE-2021-28799?

CVE-2021-28799 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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