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Findings

CVE-2021-28799

QNAP NAS Improper Authorization Vulnerability

Published May 12, 2021 · updated Jun 16, 2026 · qnap 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 .

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

Required action

Apply updates per vendor instructions.

CISA due date Apr 21, 2022

Affected

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

Sources

  • CISA KEVCVE-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.orgCVE-2021-28799

    Official CVE identifier

    cve.org
  • FIRST EPSSCVE-2021-28799

    30-day exploitation probability 78.3%

    first.org
  • NIST NVDCVE-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

References