CVE-2021-28809

Missing Authentication for Critical Function in RTRR Server in HBS3

CRITICAL

9.8

CVSS Score

Published: July 8, 2021 at 07:40 AM UTC

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

2 products affected across 1 vendorHybrid Backup SyncQTS

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Severity

CRITICAL9.8

Exploit prediction

EPSS 16%

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

Affected

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

Hybrid Backup Sync · Qnap

95%

v < 3.0.210506v < 3.0.210507v < v3.0.210506v < v3.0.210507

Affected range stops below 3.0.210506, so it looks safe — our inference, not a vendor statement

Affected range stops below 3.0.210507, so it looks safe — our inference, not a vendor statement

Affected range stops below v3.0.210506, so it looks safe — our inference, not a vendor statement

Affected range stops below v3.0.210507, so it looks safe — our inference, not a vendor statement

qnap-qts (environment)

QTS · 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-21-19

References (2)

x_refsource_MISCVendor Advisory

Source: [email protected]

https://www.qnap.com/en/security-advisory/qsa-21-19

x_refsource_MISCThird Party AdvisoryVDB Entry

Source: [email protected]

https://www.zerodayinitiative.com/advisories/ZDI-21-783/

CVSS

9.8CRITICALqnap

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

Vector?

Quick Info

StatusMODIFIED

CWE

CWE-284CWE-306CWE-749

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