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CVE-2021-28799

QNAP NAS Improper Authorization

10.0 CRITICALActively exploited (CISA KEV)Used in ransomwareEPSS 78.3%
  1. Published13 May 2021
  2. Added to CISA KEV31 Mar 2022
  3. Remediation due21 Apr 2022
Actively exploited (CISA KEV)

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

Added to KEV: 31 Mar 2022Federal remediation due: 21 Apr 2022Used in ransomware

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 .

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeChanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Affected products

QNAP Hybrid Backup Sync< 16.0.0415 · < 16.0.0419 · < 3.0.210411 · < 3.0.210412

Remediation

Fixed in
QNAP Hybrid Backup Sync≥ 16.0.0415

References

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Frequently asked

Is CVE-2021-28799 being actively exploited?

Yes. CVE-2021-28799 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added 31 Mar 2022. It has been used in ransomware campaigns.

How severe is CVE-2021-28799?

CVE-2021-28799 has a CVSS 3.1 base score of 10.0, rated critical. EPSS estimates a 78.3% probability of exploitation.

Which products are affected by CVE-2021-28799?

Affected products include QNAP Hybrid Backup Sync.

How do I fix CVE-2021-28799?

Upgrade affected software to a fixed version, for example QNAP Hybrid Backup Sync 16.0.0415 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2021-28799 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. Because it is on the CISA KEV list, Secuno flags any affected asset as top-priority automatically. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.