{
  "id": "CVE-2021-28799",
  "url": "https://spydr.io/cve/CVE-2021-28799",
  "published": "2021-05-13T03:15:06.843Z",
  "modified": "2026-06-17T03:46:53.003Z",
  "score": 9.8,
  "severity": "critical",
  "cvss_version": "3.1",
  "vector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
  "score_source": "NVD",
  "epss": 0.7825,
  "epss_percentile": 0.99571,
  "exploited": true,
  "kev": {
    "added": "2022-03-31",
    "due": "2022-04-21",
    "action": "Apply updates per vendor instructions.",
    "ransomware": "Known",
    "name": "QNAP NAS Improper Authorization Vulnerability",
    "notes": "https://nvd.nist.gov/vuln/detail/CVE-2021-28799"
  },
  "ssvc_exploitation": "active",
  "vendors": [
    "QNAP Systems Inc."
  ],
  "products": [
    "QNAP Systems Inc. HBS 3",
    "QNAP Systems Inc. HBS 2",
    "QNAP Systems Inc. HBS 1.3"
  ],
  "cwes": [
    "CWE-285"
  ],
  "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 .",
  "status": "Analyzed",
  "score_type": "Primary",
  "scores": {
    "cvss_v40": null,
    "cvss_v31": 9.8,
    "cvss_v30": null
  },
  "references": [
    {
      "url": "https://www.qnap.com/en/security-advisory/QSA-21-13",
      "tags": [
        "Vendor Advisory"
      ]
    },
    {
      "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-28799",
      "tags": [
        "US Government Resource"
      ]
    }
  ],
  "nvd_url": "https://nvd.nist.gov/vuln/detail/CVE-2021-28799",
  "covered_in": [],
  "attribution": [
    {
      "source": "NVD",
      "url": "https://nvd.nist.gov",
      "notice": "This product uses data from the NVD API but is not endorsed or certified by the NVD."
    },
    {
      "source": "CISA KEV",
      "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog",
      "notice": "Known exploited vulnerabilities from the CISA KEV catalog."
    },
    {
      "source": "FIRST EPSS",
      "url": "https://www.first.org/epss",
      "notice": "Exploit prediction scores from FIRST EPSS."
    }
  ]
}