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Vulnerabilities

Vulnerability · CVE-2021-28799

QNAP NAS Improper Authorization Vulnerability

Published Apr 29, 2021 · catalog updated Jun 16, 2026 · QNAP QNAP Network-Attached Storage (NAS)

Patch now

CVE-2021-28799 is in the CISA known-exploited catalog, due Apr 21, 2022. Confirm QNAP QNAP Network-Attached Storage (NAS) against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Gaps on this record

  • No version range is stored. A customer cannot check an installed version against this record.
Severity
Critical9.8
Known exploitation
CISA KEV and VulnCheck KEV
EPSS
78.25%
Remediation
Remediation guidance
Affected products
cpe qnap/hybrid backup sync · vendor QNAP Network Attached Storage (NAS) · vendor QNAP QNAP Network-Attached Storage (NAS)

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 .

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe qnap/hybrid backup syncversion unspecified
  • vendor QNAP Network Attached Storage (NAS)version unspecified
  • vendor QNAP QNAP Network-Attached Storage (NAS)version unspecified

How to fix CVE-2021-28799

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

CVE-2021-28799 is in the CISA known-exploited catalog, due Apr 21, 2022. Confirm QNAP QNAP Network-Attached Storage (NAS) against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Which versions are affected?

Affected version ranges are not on this record. Apply updates per vendor instructions.

What should an analyst verify?

CWE-285: Improper Authorization. EPSS 78.25%. The CISA KEV listing is the exploitation evidence. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. May 12, 2021 · Catalog

    Detected

    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

  2. Mar 31, 2022 · CISA KEV

    Known exploited

    Apply updates per vendor instructions.

  3. Apr 21, 2022 · CISA KEV

    Remediation due

    Apply updates per vendor instructions.

  4. Jun 16, 2026 · Catalog

    Updated

    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

Sources

  • CISA KEVConfirmed exploitationCVE-2021-28799

    QNAP NAS running HBS 3 contains an improper authorization vulnerability which can allow remote attackers to log in to a device.

    cisa.gov
  • CVE.orgVulnerability recordCVE-2021-28799

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2021-28799

    30-day exploitation probability 78.3%

    first.org
  • NIST NVDVulnerability recordCVE-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;

    nvd.nist.gov
  • VulnCheck KEVConfirmed exploitationCVE-2021-28799

    QNAP NAS running HBS 3 contains an improper authorization vulnerability which can allow remote attackers to log in to a device.

    vulncheck.com

References

Freshness

Last verified in this catalog Oct 17, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.