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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 21 Apr 2022. Known ransomware use
Hybrid Backup SyncApplication · Qnap

CVE-2021-28799

CRITICAL · 9.8 CVSS v3.1 Published 2021-05-13
Fix available
A fix is available. Upgrade to 3.0.210411 / 3.0.210412 or later.
See remediation →
100/100
Remediation priority · Urgent
In the wild Ransomware High EPSS Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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 .

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

An improper authorization vulnerability in QNAP HBS 3 (Hybrid Backup Sync 3) allows remote attackers to bypass authentication and log in to affected NAS devices. This is a critical network-exploitable flaw requiring no privileges, affecting multiple QTS and QuTS hero/cloud versions prior to the patched releases.

MitigationUpdate HBS 3 to the patched version specific to the QTS/QuTS version in use (v16.0.0415 for QTS 4.5.2, v3.0.210412 for QTS 4.3.6, v3.0.210411 for QTS 4.3.4/4.3.3, or v16.0.0419 for QuTS hero/cloud).

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Hybrid Backup SyncApplication
Affected:< 16.0.0415< 3.0.210412< 3.0.210411< 16.0.0419

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Verify HBS 3 is installed
    Log into QNAP QTS/QuTS admin console, open App Center, and search for Hybrid Backup Sync (HBS 3). If not installed, the vulnerability does not apply.
    Affected if HBS 3 application is present on the NAS system
  2. Check installed HBS 3 version
    In App Center, click on HBS 3 and view the version information. Alternatively, access the NAS via SSH and run: /sbin/getcfg hbs3 version (or check via qpkg command)
    Affected if The displayed version number falls below any of these thresholds: 16.0.0415, 3.0.210412, 3.0.210411, or 16.0.0419 depending on your QTS/QuTS version
  3. Confirm HBS 3 web service is accessible
    Test if the HBS 3 web interface is reachable externally by attempting to access https://[NAS-IP]:8080/hbs3/ or the default HBS port (ensure port is open in Router/Firewall settings)
    Affected if The HBS 3 web interface is exposed to untrusted networks and the installed version is vulnerable
  4. Review network exposure of HBS 3
    In QTS, go to Control Panel > Security > Security Level and check if HBS 3 services are accessible from external networks. Also verify Router configuration for port forwarding rules targeting HBS ports.
    Affected if HBS 3 is accessible from the internet or untrusted LAN segments and version is below the fixed releases

If HBS 3 is installed and its version is below 16.0.0415 (or 3.0.210412/3.0.210411/16.0.0419 depending on QTS version), the NAS is vulnerable to pre-authentication remote login bypass.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 3.0.210411 / 3.0.210412 / 16.0.0415 or later
Fixed in 3.0.2104113.0.21041216.0.0415
Interim mitigation

Update HBS 3 to the patched version specific to the QTS/QuTS version in use (v16.0.0415 for QTS 4.5.2, v3.0.210412 for QTS 4.3.6, v3.0.210411 for QTS 4.3.4/4.3.3, or v16.0.0419 for QuTS hero/cloud).

Recommended fix High confidence

HBS 3: v16.0.0415+ (QTS 4.5.2), v3.0.210412+ (QTS 4.3.6), v3.0.210411+ (QTS 4.3.4/4.3.3), v16.0.0419+ (QuTS hero/QuTScloud)

  1. 1. Identify the QTS or QuTS hero/QuTScloud version running on the QNAP NAS device
  2. 2. Navigate to the QNAP App Center or HBS 3 application
  3. 3. Check the current Hybrid Backup Sync (HBS 3) version installed
  4. 4. If running QTS 4.5.2, upgrade HBS 3 to version 16.0.0415 or later
  5. 5. If running QTS 4.3.6, upgrade HBS 3 to version 3.0.210412 or later
  6. 6. If running QTS 4.3.4 or 4.3.3, upgrade HBS 3 to version 3.0.210411 or later
  7. 7. If running QuTS hero h4.5.1 or QuTScloud c4.5.1-c4.5.4, upgrade HBS 3 to version 16.0.0419 or later
  8. 8. Verify the upgrade was successful and the new version is running
Caveat Review QNAP release notes for any breaking changes or migration requirements before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Hybrid Backup Sync Exploited in the wild — priority engagement
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,590
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-28799 in production — separate from our analysis above.

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What this is

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  • Version or environment caveats, and links to real fixes
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