Is CVE-2021-28809 actively exploited?

No active exploitation of CVE-2021-28809 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2021-28809 be exploited remotely?

Yes. CVE-2021-28809 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2021-28809?

CVE-2021-28809 has a CVSS score of 9.8 (CRITICAL).

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CRITICAL

CVE-2021-28809

CWE-284Published: July 8, 2021· Updated: Jun 17, 2026

9.8

CVSS v3.1

Official Description

An improper access control vulnerability has been reported to affect certain legacy versions of HBS 3. If exploited, this vulnerability allows attackers to compromise the security of the operating system.QNAP have already fixed this vulnerability in the following versions of HBS 3: QTS 4.3.6: HBS 3 v3.0.210507 and later QTS 4.3.4: HBS 3 v3.0.210506 and later QTS 4.3.3: HBS 3 v3.0.210506 and later

NVD Source

Technical Analysis

CVE-2021-28809 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.8.