CVE-2021-28799

Improper Authorization Vulnerability in HBS 3 (Hybrid Backup Sync)

CRITICAL

9.8

CVSS Score

Published: May 13, 2021 at 02:55 AM UTC

Updated: June 17, 2026 at 03:46 AM UTC

4 products affected across 1 vendorHybrid Backup SyncQTSQuTS hero

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Severity

CRITICAL9.8

Exploitation

CISA KEV

Exploit prediction

EPSS 78%

SSVC

Active

Actively Exploited

CISA Known Exploited Vulnerabilities (KEV) Catalog

EPSS Score78.3%

EPSS (Exploit Prediction Scoring System) estimates a 78.3% chance this CVE is exploited in the wild within the next 30 days — higher than 100% of all CVEs. It complements CVSS: a high EPSS on a mid-severity CVE can still be urgent.

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

Required Action

Apply updates per vendor instructions.

Ransomware Use

Known

Added to KEV

Mar 31, 2022

Remediation Due

Apr 21, 2022

1654 days overdue

Notes

https://nvd.nist.gov/vuln/detail/CVE-2021-28799

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 .

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Hybrid Backup Sync · Qnap

95%

v < 16.0.0415v < 16.0.0419v < 3.0.210411v < 3.0.210412v < v16.0.0415v < v16.0.0419v < v3.0.210411v < v3.0.210412

Vendor states this is fixed in 1.3 (unaffected)

Affected range stops below 16.0.0415, so it looks safe — our inference, not a vendor statement

Affected range stops below 16.0.0419, so it looks safe — our inference, not a vendor statement

Vendor states this is fixed in 2 (unaffected)

Affected range stops below 3.0.210411, so it looks safe — our inference, not a vendor statement

Affected range stops below 3.0.210412, so it looks safe — our inference, not a vendor statement

Affected range stops below v16.0.0415, so it looks safe — our inference, not a vendor statement

Affected range stops below v16.0.0419, so it looks safe — our inference, not a vendor statement

Affected range stops below v3.0.210411, so it looks safe — our inference, not a vendor statement

Affected range stops below v3.0.210412, so it looks safe — our inference, not a vendor statement

qnap-qts (environment) · qnap-quts-hero (environment) · qnap-qutscloud (environment)

QTS · Qnapdevice

80%

All versions

QuTS hero · Qnapdevice

80%

All versions

QuTScloud · Qnapdevice

80%

All versions

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://www.qnap.com/en/security-advisory/QSA-21-13

References (2)

x_refsource_MISCVendor Advisory

Source: [email protected]

https://www.qnap.com/en/security-advisory/QSA-21-13

US Government Resource

Source: 134c704f-9b21-4f2e-91b3-4a467353bcc0

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-28799

SSVC — Action Prioritization

SSVCActiveAutomatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

9.8CRITICAL[email protected]

Attack Vector: NETWORK
Complexity: LOW
Privileges: NONE
User Interaction: NONE
Scope: UNCHANGED
Confidentiality: HIGH
Integrity: HIGH
Availability: HIGH

Vector?

Quick Info

StatusANALYZED

CWE

CWE-285NVD-CWE-Other

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