What’s Vulnerable › Vulnerabilities

CVE-2021-28809: Missing Authentication for Critical Function in RTRR Server in HBS3

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 16.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-07-08 · updated 2026-06-17
• Weakness: CWE-284

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 products

• QNAP Systems Inc. HBS 3 Hybrid Backup Sync: before 3.0.210507; before 3.0.210506 — fixed in 3.0.210506, 3.0.210507

How to fix

Upgrade to a fixed version: QNAP Systems Inc. HBS 3 Hybrid Backup Sync 3.0.210506, 3.0.210507. Check the vendor advisory for mitigations.

References

• https://www.qnap.com/en/security-advisory/qsa-21-19
• https://www.zerodayinitiative.com/advisories/ZDI-21-783/
• https://www.qnap.com/en/security-advisory/qsa-21-19
• https://www.zerodayinitiative.com/advisories/ZDI-21-783/

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