CVE-2021-28806Network attack vector

Authenticated script execution via undisclosed DOM handling

Published Jun 3, 2021 · Updated Sep 16, 2024

DOM-based XSS in QNAP QTS, QuTS hero, and QuTScloud allows remote authenticated users to execute script in a user's browser. QNAP has not disclosed the affected client-side DOM source, sink, or the unsafe operation that transfers attacker-controlled data between them. Exploitation requires low-privileged access and user interaction; injected script runs in the NAS web interface's browser context and can read data exposed there.

CVSS severity5.7
Medium
EPSS probability0.51%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

DOM-based XSS in QNAP QTS, QuTS hero, and QuTScloud allows remote authenticated users to execute script in a user's browser. QNAP has not disclosed the affected client-side DOM source, sink, or the unsafe operation that transfers attacker-controlled data between them. Exploitation requires low-privileged access and user interaction; injected script runs in the NAS web interface's browser context and can read data exposed there.

The record

CVE
CVE-2021-28806
Published
Jun 3, 2021
Updated
Sep 16, 2024
Vendor
Linn Products Limited
Product
QuTS hero
Classifications
CWE-79, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 3, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <h4.5.2.1638 Build 20210414

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Linn Products Limited · QuTS heroversion=unspecified <h4.5.2.1638 Build 20210414
Linn Products Limited · QuTScloudversion=unspecified <c4.5.5.1656 Build 20210503
Linn Products Limited · QTSversion=unspecified <4.5.3.1652 Build 20210428

Published CVSS scores

5.7QNAP Systems, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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