No exploitation reportedFix available

CVE-2021-28800

Q: Is CVE-2021-28800 actively exploited?

Active exploitation of CVE-2021-28800 has not been confirmed. Its EPSS score was 1.4% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-28800?

CVE-2021-28800 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

No exploitation reported by the sources we read.

Published2021-06-24
Fixed in4.3.6.1663 · 4.3.3.1624
WeaknessCWE-78

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

A command injection vulnerability has been reported to affect QNAP NAS running legacy versions of QTS. If exploited, this vulnerability allows attackers to execute arbitrary commands in a compromised application. This issue affects: QNAP Systems Inc. QTS versions prior to 4.3.6.1663 Build 20210504; versions prior to 4.3.3.1624 Build 20210416. This issue does not affect: QNAP Systems Inc. QTS 4.5.3. QNAP Systems Inc. QuTS hero h4.5.3. QNAP Systems Inc. QuTScloud c4.5.5.

Timeline

dates in UTC

2021-06-2407:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-28800?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-28800?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Qnap qts

Branch	Affected	Fixed in	Source
4.3	≥ 4.3.4, < 4.3.6.1663	4.3.6.1663	NVD
4.3	< 4.3.3.1624	4.3.3.1624	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Update Qnap qts to 4.3.6.1663 · 4.3.3.1624

Advisories and patches

www.qnap.comVendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

CNACVSS 3.18.1read 2026-10-23
NVDCVSS 3.19.8read 2026-10-23
NVDCVSS 2.07.5read 2026-10-23
CNAweakness (CWE)CWE-78read 2026-10-23
FIRST EPSSEPSS score1.4 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published: 2021-06-24
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-28800?

Is CVE-2021-28800 actively exploited?

Active exploitation of CVE-2021-28800 has not been confirmed. Its EPSS score was 1.4% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-28800?

CVE-2021-28800 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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