Critical 10.0Known exploited (CISA KEV)Published May 13, 2021

CVE-2021-28799Improper Authorization Vulnerability in HBS 3 (Hybrid Backup Sync)

Updated under an hour ago (2026-10-19 07:10 UTC)

Does this affect you?

It affects QNAP Systems Inc. HBS 3 and 3 other products. Add what you run to find out whether that includes you.

CISA lists it as known exploited since Mar 31, 2022; federal agencies had to remediate by Apr 21, 2022, and it is known to be used in ransomware. Treat that date as your deadline.

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Every CVE for QNAP Systems Inc. HBS 3

Exploited in the last 30 days

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 .

CVSS: 10.0 CRITICAL (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Weakness (CWE): CWE-285
Known exploited: Added to CISA KEV Mar 31, 2022; federal remediation due Apr 21, 2022; known ransomware useApply updates per vendor instructions.
EPSS (exploitation in the next 30 days): 78.25% (percentile 100)
Assigned by: qnap
NVD analysis: Analyzed
Record last updated: Oct 21, 2025
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

QNAP Systems Inc. HBS 3 qnap_systems:hbs_3 (from the name)	from unspecified before v16.0.0415	CNA record
QNAP Systems Inc. HBS 2 qnap_systems:hbs_2 (from the name)	all versions not affected	CNA record
QNAP Systems Inc. HBS 1.3 qnap_systems:hbs_1.3 (from the name)	all versions not affected	CNA record
qnap hybrid_backup_sync qnap:hybrid_backup_sync	before 16.0.0415; before 3.0.210412; before 3.0.210411; before 16.0.0419; before 16.0.0419	NVD

References

https://www.qnap.com/en/security-advisory/QSA-21-13x-refsource-misc, vendor-advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-28799us-government-resource

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.