{"id":"CVE-2021-28799","url":"https://www.cyber-defence.io/tools/cve/CVE-2021-28799","generatedAt":"2026-10-27T22:32:04.466Z","title":"QNAP NAS Improper Authorization Vulnerability","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 .","published":"2021-05-13T03:15:07.000Z","lastModified":"2026-06-17T03:46:53.000Z","status":"Analyzed","sourceIdentifier":"security@qnapsecurity.com.tw","cvss":{"version":"3.1","score":9.8,"severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"},"cwe":["CWE-285"],"affected":["qnap/hybrid backup sync"],"epss":{"score":0.7825,"percentile":0.99576,"date":"2026-10-26","history":[]},"kev":{"listed":true,"dateAdded":"2022-03-31","dueDate":"2022-04-21","knownRansomwareCampaignUse":"Known","notes":"Apply updates per vendor instructions.\nhttps://nvd.nist.gov/vuln/detail/CVE-2021-28799"},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"urgent","text":"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."},"changes":[],"references":[{"url":"https://www.qnap.com/en/security-advisory/QSA-21-13","tags":["Vendor Advisory"],"source":"security@qnapsecurity.com.tw"},{"url":"https://www.qnap.com/en/security-advisory/QSA-21-13","tags":["Vendor Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-28799","tags":["US Government Resource"],"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2021-28799","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}