QNAP NAS Improper Authorization Vulnerability
QNAP NAS running HBS 3 contains an improper authorization vulnerability which can allow remote attackers to log in to a device.
- Vendor
- QNAP
- Product
- Network Attached Storage (NAS)
- CVSS
- 10.0
- EPSS (exploit probability)
- 78.3%
- Status
- kevransomware use
- CISA patch-by (BOD 22-01)
- Added to KEV
Is CVE-2021-28799 being exploited?
Yes. CISA added CVE-2021-28799 to its Known Exploited Vulnerabilities catalog on . CISA only lists a CVE when it has reliable evidence of exploitation in the wild. CISA marks it as known to be used in ransomware campaigns.
FIRST's EPSS model puts the probability of exploitation activity in the next 30 days at 78.3% (scored October 14, 2026).
- CISA KEV[ LISTED ]
- ENISA EUVD (exploited)[ — ]
- CIRCL KEV[ — ]
Catalog snapshot 2026-10-21. Full cross-catalog view: /kev-comparison
What to do
CISA required actionApply updates per vendor instructions.
US federal civilian agencies must remediate by (21 days after listing) under BOD 22-01. Everyone else: that deadline is a sensible upper bound, not a target. Vendor guidance and the NVD record are linked under Source above.
Other QNAP Network Attached Storage (NAS) CVEs we track
| CVE / Vulnerability | Severity | CVSS | EPSS | Added to KEV |
|---|---|---|---|---|
| CVE-2018-19953 QNAP NAS File Station Cross-Site Scripting Vulnerabilityransomware use | [ MEDIUM ] | 6.1 | 29.0% | |
| CVE-2018-19949 QNAP NAS File Station Command Injection Vulnerabilityransomware use | [ CRITICAL ] | 9.8 | 28.6% | |
| CVE-2018-19943 QNAP NAS File Station Cross-Site Scripting Vulnerabilityransomware use | [ HIGH ] | 8.0 | 21.5% | |
| CVE-2020-2509 QNAP Network-Attached Storage (NAS) Command Injection Vulnerability | [ CRITICAL ] | 9.8 | 34.0% |