{"id":"CVE-2021-28809","url":"https://www.cyber-defence.io/tools/cve/CVE-2021-28809","generatedAt":"2026-10-27T20:20:13.142Z","title":"An improper access control vulnerability has been reported to affect certain legacy versions of HBS 3.","description":"An improper access control vulnerability has been reported to affect certain legacy versions of HBS 3. If exploited, this vulnerability allows attackers to compromise the security of the operating system.QNAP have already fixed this vulnerability in the following versions of HBS 3: QTS 4.3.6: HBS 3 v3.0.210507 and later QTS 4.3.4: HBS 3 v3.0.210506 and later QTS 4.3.3: HBS 3 v3.0.210506 and later","published":"2021-07-08T08:15:08.000Z","lastModified":"2026-06-17T03:46:54.000Z","status":"Modified","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-284","CWE-306","CWE-749"],"affected":["qnap/hybrid backup sync"],"epss":{"score":0.16093,"percentile":0.96899,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"urgent","text":"EPSS puts the probability of exploitation in the next 30 days at 16.1%, higher than 97% of all known CVEs. Patch or mitigate before the next change window."},"changes":[],"references":[{"url":"https://www.qnap.com/en/security-advisory/qsa-21-19","tags":["Vendor Advisory"],"source":"security@qnapsecurity.com.tw"},{"url":"https://www.zerodayinitiative.com/advisories/ZDI-21-783/","tags":["Third Party Advisory","VDB Entry"],"source":"security@qnapsecurity.com.tw"},{"url":"https://www.qnap.com/en/security-advisory/qsa-21-19","tags":["Vendor Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.zerodayinitiative.com/advisories/ZDI-21-783/","tags":["Third Party Advisory","VDB Entry"],"source":"af854a3a-2127-422b-91ae-364da2661108"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2021-28809","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."}