CVE-2021-28809

highpriority · attend · 45OT risk · highEPSS 0.161 · 97 %ileEURUUS

grimoire priorityP1 · Urgent

Exploitable?

—

no known exploitation

Likely / severe?

16.1% (97th) EPSS

CVSS 10 · high

Is it mine?

9 products

Check your exposure

Who says so?

4 sources

cnnvd · enisa_euvd · fstec_bdu · nvd

EPSS · scored 2026-10-27

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

cvss

Technical severity, 0–10. One row per scoring source.

10.0

010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · high–critical · 9–10

v2.010highAV:N/AC:L/Au:N/C:C/I:C/A:Cprimary · NVD / NIST USexploitability 10 · impact 10

v3.19.8criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hprimary · NVD / NIST USexploitability 3.9 · impact 5.9

v3.19.8criticalAV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsecondary · FSTEC (BDU) RU

v3.19.8criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsecondary · ENISA EU

v3.19.8criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsecondary · security@qnapsecurity.com.twexploitability 3.9 · impact 5.9

v3.19criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:Usecondary · CVSS-BT (t0sche)

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-284USCWE-284USCWE-306USCWE-306USCWE-749USCWE-749US

affected products (9)

Products and version ranges known to be affected.

QNAP Systems Inc. HBS 3unspecified → v3.0.210506enisa_euvdEU
QNAP Systems Inc. HBS 3unspecified → v3.0.210507enisa_euvdEU
QNAP Systems, Inc. HBS 3 (Hybrid Backup Sync)≤ 3.0.210506 for QTS 4.3.3 and QTS 4.3.4fstec_bduRU
QNAP Systems, Inc. HBS 3 (Hybrid Backup Sync)≤ 3.0.210507fstec_bduRU
QNAP Systems, Inc. QTS≤ 4.3.6fstec_bduRU
QNAP Systems, Inc. QTS≤ 4.3.3fstec_bduRU
QNAP Systems, Inc. QTS≤ 4.3.4fstec_bduRU
qnap hybrid backup sync< 3.0.210506nvdUScpe:2.3:a:qnap:hybrid_backup_sync:*:*:*:*:*:*:*:*
qnap hybrid backup sync< 3.0.210507nvdUScpe:2.3:a:qnap:hybrid_backup_sync:*:*:*:*:*:*:*:*

also known as (6)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd fstec_bdu nvd NVD CVE.org MITRE

published 2021-07-08modified 2026-06-17

references (7)

External citations — patches, advisories, analysis.

scry

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