What is CVE-2021-47857?

CVE-2021-47857 is a high-severity vulnerability in Moodle, classified under Cross-site Scripting. CVSS score: 7.2/10. Published 2026-01-21.

How severe is CVE-2021-47857?

High severity. CVSS v3 base score is 7.2 out of 10.

XSS in Moodle

CVE-2021-47857

Moodle 3.10.3 contains a persistent cross-site scripting vulnerability in the calendar event subtitle field that allows attackers to inject malicious scripts. Attackers can craft a calendar event with malicious JavaScript in the subtitle track label to execute arbitrary code when users view the event.

Vulnerability class: XSS (Cross-Site Scripting)

EPSS: 0.003 (23.3th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 7.2 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N.

Affected products

Moodle — versions 3.10.3

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

disclosure@vulncheck.com (Exploit, VDB Entry, Third Party Advisory, exploit)
disclosure@vulncheck.com (Product, product)
disclosure@vulncheck.com (Third Party Advisory, third-party-advisory)

Frequently asked questions

What is CVE-2021-47857?: CVE-2021-47857 is a high-severity vulnerability in Moodle, classified under Cross-site Scripting. CVSS score: 7.2/10. Published 2026-01-21.
How severe is CVE-2021-47857?: High severity. CVSS v3 base score is 7.2 out of 10.