Answer in brief
CVE-2021-28799 records a High severity vulnerability in Improper Authorization Vulnerability in HBS 3 (Hybrid Backup Sync). The current sources mark it as known exploited. The current feed maps QNAP Systems Inc./HBS 3 (generic), QNAP Systems Inc./HBS 3 (generic), QNAP Systems Inc./HBS 3 (generic), QNAP Systems Inc./HBS 3 (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
A CVSS score is not reported in the current record. Known-exploitation status makes exposure review time-sensitive. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps QNAP Systems Inc./HBS 3 (generic), QNAP Systems Inc./HBS 3 (generic), QNAP Systems Inc./HBS 3 (generic), QNAP Systems Inc./HBS 3 (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| QNAP Systems Inc./HBS 3generic | >=unspecified <v16.0.0415 | v16.0.0415 |
| QNAP Systems Inc./HBS 3generic | >=unspecified <v3.0.210412 | v3.0.210412 |
| QNAP Systems Inc./HBS 3generic | >=unspecified <v3.0.210411 | v3.0.210411 |
| QNAP Systems Inc./HBS 3generic | >=unspecified <v16.0.0419 | v16.0.0419 |
Published upstream
May 13, 2021
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Oct 21, 2025
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
May 24, 2026
Added to CISA KEV
Mar 31, 2022
Evidence: source:kev:kev:kev:recordAn 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 .
Quoted source text, attributed separately from HOL analysis.
Answer in brief
CVE-2021-28799 records a High severity vulnerability in Improper Authorization Vulnerability in HBS 3 (Hybrid Backup Sync). The current sources mark it as known exploited. The current feed maps QNAP Systems Inc./HBS 3 (generic), QNAP Systems Inc./HBS 3 (generic), QNAP Systems Inc./HBS 3 (generic), QNAP Systems Inc./HBS 3 (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
A CVSS score is not reported in the current record. Known-exploitation status makes exposure review time-sensitive. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps QNAP Systems Inc./HBS 3 (generic), QNAP Systems Inc./HBS 3 (generic), QNAP Systems Inc./HBS 3 (generic), QNAP Systems Inc./HBS 3 (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| QNAP Systems Inc./HBS 3generic | >=unspecified <v16.0.0415 | v16.0.0415 |
| QNAP Systems Inc./HBS 3generic | >=unspecified <v3.0.210412 | v3.0.210412 |
| QNAP Systems Inc./HBS 3generic | >=unspecified <v3.0.210411 | v3.0.210411 |
| QNAP Systems Inc./HBS 3generic | >=unspecified <v16.0.0419 | v16.0.0419 |
Published upstream
May 13, 2021
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Oct 21, 2025
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
May 24, 2026
Added to CISA KEV
Mar 31, 2022
Evidence: source:kev:kev:kev:recordAn 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 .
Quoted source text, attributed separately from HOL analysis.