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)
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.004 (28.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 28th percentile — 28.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.004 · change: +0.000
Affected products
- Moodle — versions 3.10.3
Weakness classification (CWE)
References
- www.exploit-db.com/exploits/49714 (Exploit, VDB Entry, Third Party Advisory, exploit)
- moodle.org/ (Product, product)
- www.vulncheck.com/advisories/moodle-label-persistent-cross-site-scripting (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.