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QtsOperating system · Qnap

CVE-2021-28800

CRITICAL · 9.8 CVSS v3.1 Published 2021-06-24
Fix available
A fix is available. Upgrade to 4.3.3.1624 / 4.3.6.1663 or later.
See remediation →
100/100
Remediation priority · Urgent
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
A command injection vulnerability has been reported to affect QNAP NAS running legacy versions of QTS. If exploited, this vulnerability allows attackers to execute arbitrary commands in a compromised application. This issue affects: QNAP Systems Inc. QTS versions prior to 4.3.6.1663 Build 20210504; versions prior to 4.3.3.1624 Build 20210416. This issue does not affect: QNAP Systems Inc. QTS 4.5.3. QNAP Systems Inc. QuTS hero h4.5.3. QNAP Systems Inc. QuTScloud c4.5.5.

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 · moderate confidence

A command injection vulnerability in QNAP QTS allows remote attackers to execute arbitrary commands by injecting malicious commands into the application. This affects legacy QTS versions prior to 4.3.6.1663 Build 20210504 and versions prior to 4.3.3.1624 Build 20210416.

MitigationUpgrade QTS to version 4.3.6.1663 Build 20210504 or later (for 4.3.6 branch) or 4.3.3.1624 Build 20210416 or later (for 4.3.3 branch), or migrate to QTS 4.5.3/QuTS hero/QuTScloud which are not affected by this vulnerability.

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
QtsOperating system
Affected:< 4.3.3.1624>= 4.3.4, < 4.3.6.1663

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. Identify QTS version via web interface
    Log into QTS as admin, go to Control Panel > System > Firmware Update, and note the displayed QTS version and build number
    Affected if Version shows 4.3.3.x below build 20210416, or 4.3.4.x/4.3.5.x below build 20210504, or any version below 4.3.3
  2. Identify QTS version via command line
    Access the NAS via SSH or terminal, then run `cat /proc/$(pgrep -f stooq)/cmdline 2>/dev/null || cat /etc/config/.firmware_version` or check the system version in QTS via `version` command if available
    Affected if Version shows 4.3.3.x below build 20210416, or 4.3.4.x/4.3.5.x below build 20210504, or any version below 4.3.3
  3. Verify build number matches vulnerable range
    If version shows 4.3.3.xxx or 4.3.6.xxx, confirm the exact build number by checking System > About in the QTS web interface
    Affected if Build number is below 20210416 for 4.3.3 branch, or below 20210504 for 4.3.4/4.3.5/4.3.6 branches
  4. Confirm QTS branch is affected
    Review the full version string which includes both the version number (e.g., 4.3.3, 4.3.4, 4.3.5, 4.3.6) and the build date
    Affected if Running any version in the 4.3.3 branch prior to 1624, or any version from 4.3.4, 4.3.5, or 4.3.6 branch prior to the fixed builds

If your QTS version is 4.3.3.x with build before 20210416, or 4.3.4/4.3.5/4.3.6 with build before 20210504, then your environment is affected by this command injection vulnerability.

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 4.3.3.1624 / 4.3.6.1663 or later
Fixed in 4.3.3.16244.3.6.1663
Interim mitigation

Upgrade QTS to version 4.3.6.1663 Build 20210504 or later (for 4.3.6 branch) or 4.3.3.1624 Build 20210416 or later (for 4.3.3 branch), or migrate to QTS 4.5.3/QuTS hero/QuTScloud which are not affected by this vulnerability.

Recommended fix High confidence

QTS 4.3.6.1663 (Build 20210504) or later; or QTS 4.5.3+ recommended

  1. 1. Back up all critical data on the QNAP NAS before proceeding with any firmware upgrade.
  2. 2. Log in to the QNAP admin interface (QTS) as an administrator.
  3. 3. Navigate to Control Panel > System > Firmware Update.
  4. 4. Select "Check for Update" to identify available firmware versions.
  5. 5. If a newer stable version is available (4.3.6.1663 Build 20210504 or later, or 4.5.3+), click to download and install the update.
  6. 6. Alternatively, download the firmware manually from the QNAP download center and use "Update manually" option.
  7. 7. Allow the system to restart automatically after the update completes.
  8. 8. Verify the new QTS version by checking Control Panel > System > Firmware Update > Version Information.
Caveat Review QNAP release notes for compatibility with installed apps and services before upgrading; legacy apps may require updates

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

Fix this in Qts Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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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-2021-28800 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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