CVE-2021-28799
Improper Authorization Vulnerability in HBS 3 (Hybrid Backup Sync)
- Published
- May 13, 2021
- Updated
- Oct 21, 2025
- Assigning CNA
- qnap
- Evidence observed
- Mar 31, 2022
Primary CVSS
nvd · CVSS 3.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:HHigh · next 30 days
- Percentile
- 99.6%
- Model date
- Oct 18, 2026
EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.
CISA Known Exploited
This CVE appears in the CISA Known Exploited Vulnerabilities catalog.
Summary
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 .
Sources
http/cves/2021/CVE-2021-28799.yaml
Nuclei TemplatesDeclared conditions
- network: http($.protocol_keys)
- verification: regex,status,word($.matchers[*].type)
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