CVE-2021-28799
QNAP NAS Improper Authorization Vulnerability
Does this matter?
Known to be exploited in the wild (CISA KEV, CISA remediation deadline 21 April 2022). Treat as an emergency change: patch or isolate now, then hunt for prior compromise.
Description
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 .
- CVSS 3.1
- 9.8 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 78.25% probability · 100th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Listed 31 March 2022 · due 21 April 2022 · used in ransomware campaigns
- Weakness
- CWE-285
- Affected
- qnap/hybrid backup sync
- Source
- security@qnapsecurity.com.tw
EPSS 78.3% since 26 October 2026; no change recorded yet. The dashed line is the ten per cent mark our analysts treat as “patch before the next change window”. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
CISA notes
Apply updates per vendor instructions. https://nvd.nist.gov/vuln/detail/CVE-2021-28799
References
- https://www.qnap.com/en/security-advisory/QSA-21-13Vendor Advisory
- https://www.qnap.com/en/security-advisory/QSA-21-13Vendor Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-28799US Government Resource
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.