CVE record · CVE-2021-28799

Improper Authorization Vulnerability in HBS 3 (Hybrid Backup Sync)

CVSS 10.0 CriticalCriticalIn CISA KEV · ransomwareEPSS 0.78 · 99th percentile

Critical, because:

In CISA’s KEV catalogue since 31 Mar 2022: it is known to be exploited.
CVSS score 10.0: 9.0 or more.
CVSS score 10.0 (7.0 or more) and EPSS 0.78 (0.1 or more): a high score and a real chance of exploitation in the next 30 days.

Published by the CVE Program (CNA: qnap) at 13 May 2021, 02:55 UTC. agentprime has not analysed this yet, so whether it affects any app is not known. This CVE names a vendor and product rather than a package, so the lockfile check doesn’t match it.

Affected products, as the CNA wrote them
Vendor	Product	Versions
QNAP Systems Inc.	HBS 3	affected unspecified to before v16.0.0415 custom
QNAP Systems Inc.	HBS 3	affected unspecified to before v3.0.210412 custom
QNAP Systems Inc.	HBS 3	affected unspecified to before v3.0.210411 custom
QNAP Systems Inc.	HBS 3	affected unspecified to before v3.0.210411 custom
QNAP Systems Inc.	HBS 3	affected unspecified to before v16.0.0419 custom
QNAP Systems Inc.	HBS 3	affected unspecified to before v16.0.0419 custom
QNAP Systems Inc.	HBS 2	unaffected all versions
QNAP Systems Inc.	HBS 1.3	unaffected all versions

Identifiers: CVE-2021-28799
CNA: qnap
Weakness (CWE): CWE-285
Tags: QNAP Systems Inc. HBS 3
QNAP Systems Inc. HBS 2
QNAP Systems Inc. HBS 1.3
Broken access control
Published: 13 May 2021
Updated: 21 Oct 2025

Not analysed yet

We haven’t published our own analysis of this CVE. If a person reviews it, this page will say what’s affected and what has to be true for it to matter.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
10.0	Critical	3.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H	CNA (qnap)

CISA KEV Listed since 31 Mar 2022: known to be exploited. CISA reports use in ransomware campaigns.
EPSS 0.78, the 99th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

This record came from the full history of the CVE Program, published 13 May 2021. New records show when each source confirmed them.

Sources

References from the CNA

www.qnap.com/en/security-advisory/QSA-21-13

Facts on this page come from the CVE List as the CNA published them, with CVSS from the sources named above, CISA KEV and FIRST EPSS. Vendors, products and versions are shown as the CNA wrote them. We don’t reproduce the CVE’s description.