What is CVE-2021-40555?

CVE-2021-40555 is a medium-severity vulnerability in Flatcore, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2023-02-16.

How severe is CVE-2021-40555?

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

XSS in Flatcore

CVE-2021-40555

Cross site scripting (XSS) vulnerability in flatCore-CMS 2.2.15 allows attackers to execute arbitrary code via description field on the new page creation form.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2023-02-16 · 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: 0.004 (35.6th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 36th percentile — 35.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000

Affected products

Flatcore — versions 2.0.7

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

github.com/flatCore/flatCore-CMS/issues/56 (Exploit, Patch, Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2021-40555?: CVE-2021-40555 is a medium-severity vulnerability in Flatcore, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2023-02-16.
How severe is CVE-2021-40555?: Medium severity. CVSS v3 base score is 5.4 out of 10.