How severe is CVE-2021-28816?

CVE-2021-28816 has a CVSS 3.x base score of 7.6, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability high.

Is CVE-2021-28816 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (56th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-28816?

CVE-2021-28816 primarily affects Qnap Qts. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-28816?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-28816 published?

CVE-2021-28816 was published on 2021-09-10 and last updated on 2026-06-17.

CVE-2021-28816

CVE-2021-28816 is a high-severity vulnerability in Qnap Qts with a CVSS 3.x base score of 7.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-787.

Key facts

Severity: High (CVSS 3.x base score 7.6)
CVSS v2: 6.5
EPSS exploit prediction: 1% (56th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-787
Affected product: Qnap Qts
Published: 2021-09-10
Last modified: 2026-06-17

Description

A stack buffer overflow vulnerability has been reported to affect QNAP device running QTS, QuTScloud, QuTS hero. If exploited, this vulnerability allows attackers to execute arbitrary code. We have already fixed this vulnerability in the following versions of QTS, QuTScloud, QuTS hero: QTS 4.5.4.1715 build 20210630 and later QTS 5.0.0.1716 build 20210701 and later QTS 4.3.3.1693 build 20210624 and later QTS 4.3.6.1750 build 20210730 and later QuTScloud c4.5.6.1755 and later QuTS hero h4.5.4.1771 build 20210825 and later

Frequently asked questions

What is CVE-2021-28816?: A stack buffer overflow vulnerability has been reported to affect QNAP device running QTS, QuTScloud, QuTS hero. If exploited, this vulnerability allows attackers to execute arbitrary code. We have already fixed this vulnerability in the following versions of QTS, QuTScloud, QuTS hero: QTS 4.5.4.1715 build 20210630 and later QTS 5.0.0.1716 build 20210701 and later QTS 4.3.3.1693 build 20210624 and later QTS 4.3.6.1750 build 20210730 and later QuTScloud c4.5.6.1755 and later QuTS hero h4.5.4.1771 build 20210825 and later
How severe is CVE-2021-28816?: CVE-2021-28816 has a CVSS 3.x base score of 7.6, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability high.
Is CVE-2021-28816 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (56th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-28816?: CVE-2021-28816 primarily affects Qnap Qts. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-28816?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-28816 published?: CVE-2021-28816 was published on 2021-09-10 and last updated on 2026-06-17.

References

https://www.qnap.com/en/security-advisory/qsa-21-33

Affected products (3)

cpe:2.3:o:qnap:qts:*:*:*:*:*:*:*:*
cpe:2.3:o:qnap:quts_hero:*:*:*:*:*:*:*:*
cpe:2.3:o:qnap:qutscloud:*:*:*:*:*:*:*:*

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