What is CVE-2021-28803?

CVE-2021-28803 is a medium-severity vulnerability in QNAP Q\'center, classified under Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS). CVSS score: 5.4/10. Published 2021-07-01.

How severe is CVE-2021-28803?

Medium severity. CVSS v3 base score is 5.4 out of 10.

XSS in QNAP Q\'center

CVE-2021-28803

This issue affects: QNAP Systems Inc. Q'center versions prior to 1.11.1004.

Published 2021-07-01 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.005 (37.9th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 38th percentile — 37.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000

Affected products

QNAP Q\'center
QNAP Systems Inc. Q'center — versions unspecified

Weakness classification (CWE)

References

www.qnap.com/zh-tw/security-advisory/qsa-21-31 (Vendor Advisory)

Frequently asked questions

What is CVE-2021-28803?: CVE-2021-28803 is a medium-severity vulnerability in QNAP Q\'center, classified under Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS). CVSS score: 5.4/10. Published 2021-07-01.
How severe is CVE-2021-28803?: Medium severity. CVSS v3 base score is 5.4 out of 10.