What is CVE-2020-21434?

CVE-2020-21434 is a medium-severity vulnerability in Maccms, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2021-10-04.

How severe is CVE-2020-21434?

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

XSS in Maccms

CVE-2020-21434

Maccms 10 contains a cross-site scripting (XSS) vulnerability in the Editing function under the Member module. This vulnerability is exploited via a crafted payload in the nickname text field.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2021-10-04 · 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 (42.0th percentile), scored 2026-10-02.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 42nd percentile — 42.0% 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

Maccms — versions 10.0

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

github.com/Ksharp12138/maccms_userinfo_xss/blob/master/maccms_xss.md (Exploit, Third Party Advisory)

Frequently asked questions

What is CVE-2020-21434?: CVE-2020-21434 is a medium-severity vulnerability in Maccms, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2021-10-04.
How severe is CVE-2020-21434?: Medium severity. CVSS v3 base score is 5.4 out of 10.