What is CVE-2020-2503?

CVE-2020-2503 is a critical-severity vulnerability in QNAP Qes, classified under Cross-site Scripting. CVSS score: 9.0/10. Published 2020-12-24.

How severe is CVE-2020-2503?

Critical severity. CVSS v3 base score is 9.0 out of 10.

XSS in QNAP Qes

CVE-2020-2503

If exploited, this stored cross-site scripting vulnerability could allow remote attackers to inject malicious code in File Station. QNAP has already fixed these issues in QES 2.1.1 Build 20201006 and later.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2020-12-24 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.0 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.008 (54.5th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 54th percentile — 54.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: +0.000

Affected products

QNAP Qes — versions 2.1.1
QNAP Systems Inc. Qes — versions unspecified

Weakness classification (CWE)

References

www.qnap.com/zh-tw/security-advisory/qsa-20-17 (Vendor Advisory)

Frequently asked questions

What is CVE-2020-2503?: CVE-2020-2503 is a critical-severity vulnerability in QNAP Qes, classified under Cross-site Scripting. CVSS score: 9.0/10. Published 2020-12-24.
How severe is CVE-2020-2503?: Critical severity. CVSS v3 base score is 9.0 out of 10.