CVE-2021-28803Network attack vector

Authenticated script execution via stored XSS

Published Jul 1, 2021 · Updated Sep 16, 2024

Stored cross-site scripting in QNAP Q'center before 1.11.1004 allows remote authenticated users to inject malicious code. QNAP has not published the affected input, storage location, output context, or operation that fails to neutralize untrusted content. Exploitation requires low-privileged access and a user to view the stored content, enabling attacker-controlled script execution in that user's browser.

CVSS severity5.4
Medium
EPSS probability0.47%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored cross-site scripting in QNAP Q'center before 1.11.1004 allows remote authenticated users to inject malicious code. QNAP has not published the affected input, storage location, output context, or operation that fails to neutralize untrusted content. Exploitation requires low-privileged access and a user to view the stored content, enabling attacker-controlled script execution in that user's browser.

The record

CVE
CVE-2021-28803
Published
Jul 1, 2021
Updated
Sep 16, 2024
Vendor
Linn Products Limited
Product
Q'center
Classifications
CWE-79, CWE-80, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 1, 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 <1.11.1004

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Linn Products Limited · Q'centerversion=unspecified <1.11.1004

Published CVSS scores

5.4NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
3.5NVDAV:N/AC:M/Au:S/C:N/I:P/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')
CWE-80Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)
T1059.007Command and Scripting Interpreter: JavaScript

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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