Medium severity · published Jan 21, 2026
CVE-2021-47857
Moodle 3.10.3 - 'label' Persistent Cross Site Scripting
6.1
CVSS
0.4%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
Low
Integrity
Low
Availability
None
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 32% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MO
Moodle · Moodle
3.10.3 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-47857
CVE.org
https://www.cve.org/CVERecord?id=CVE-2021-47857
Product
https://moodle.org/
Exploit
https://www.exploit-db.com/exploits/49714
Third Party Advisory
https://www.vulncheck.com/advisories/moodle-label-persistent-cross-site-scripting
More from Moodle
10.0
CVE-2019-3809
A flaw was found in Moodle versions 3.1 to 3.1.15 and earlier unsupported versions
9.8
CVE-2025-67856
Moodle: moodle: privilege escalation via incomplete role checks in badge awarding
9.8
CVE-2025-26533
SQL injection risk in course search module list filter
9.8
CVE-2024-33999
moodle: unsafe direct use of $_SERVER['HTTP_REFERER'] in admin/tool/mfa/index.php
9.8
CVE-2023-5550
Moodle: rce due to lfi risk in some misconfigured shared hosting environments