CVE-2021-28806

MEDIUMNVD 5.75.7—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.7 under NVD CVSS v3. EPSS exploit probability: 0.5%, top 60% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
5.7EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 1%CVSS: 5.7Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

A DOM-based XSS vulnerability has been reported to affect QNAP NAS running QTS and QuTS hero. If exploited, this vulnerability allows attackers to inject malicious code. This issue affects: QNAP Systems Inc. QTS versions prior to 4.5.3.1652 Build 20210428. QNAP Systems Inc. QuTS hero versions prior to h4.5.2.1638 Build 20210414. QNAP Systems Inc. QuTScloud versions prior to c4.5.5.1656 Build 20210503. This issue does not affect: QNAP Systems Inc. QTS 4.3.6; 4.3.3.

CVSS v3
5.7
EG Score
5.7(medium)
EG Risk
30(Track)
EG Risk 30/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity57% × 45%
Exploitation1% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
1%
EPSS %ILE
41%
KEV
Not listed

Published

June 3, 2021

Last Modified

November 21, 2024

References (2)

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 5× in last 7d / 29× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 162 total refreshes for this CVE.

  1. 2026-09-24 14:00 UTCEPSS rescore
  2. 2026-09-23 13:44 UTCEPSS rescore
  3. 2026-09-21 20:28 UTCEPSS rescore
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  1. 2026-08-30 01:19 UTCEPSS rescore
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  40. 2026-07-23 01:59 UTCEG score recompute
  41. 2026-07-22 22:46 UTCEG score recompute
  42. 2026-07-22 14:06 UTCEPSS rescore
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  73. 2026-07-02 16:57 UTCEPSS rescore
  74. 2026-07-01 15:03 UTCEPSS rescore
  75. 2026-06-30 23:20 UTCEPSS rescore

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Frequently asked(5)

What is CVE-2021-28806?
CVE-2021-28806 is a medium vulnerability published on June 3, 2021. A DOM-based XSS vulnerability has been reported to affect QNAP NAS running QTS and QuTS hero. If exploited, this vulnerability allows attackers to inject malicious code. This issue affects: QNAP Systems Inc. QTS versions prior to 4.5.3.1652 Build 20210428. QNAP Systems Inc. QuTS hero versions prior…
When was CVE-2021-28806 disclosed?
CVE-2021-28806 was first published in the National Vulnerability Database on June 3, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-28806 actively exploited?
CVE-2021-28806 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1% probability of exploitation in the next 30 days, which ranks it in the top 59.5% of all scored CVEs.
What is the CVSS score of CVE-2021-28806?
CVE-2021-28806 has a CVSS v3 base score of 5.7 (NVD).
How do I remediate CVE-2021-28806?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-28806, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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