What is the CVSS score of CVE-2021-47857?

CVE-2021-47857 has a CVSS 3.1 base score of 7.2 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N. EPSS exploitation probability: 0.0%.

Which versions of Moodle are affected by CVE-2021-47857?

Organizations using Moodle 3.10.3 face moderate risk from CVE-2021-47857, a cross-site scripting vulnerability rated CVSS 7.2.

Is there a public PoC exploit available for CVE-2021-47857?

Yes, a public proof-of-concept exploit is available for CVE-2021-47857. Prioritise patching immediately. EPSS: 0.0%.

How to fix or mitigate CVE-2021-47857?

Within 7 days: Identify all affected systems and apply vendor patches promptly. Verify anti-CSRF tokens and content security policies are enforced.

Moodle CVE-2021-47857

HIGH

Cross-site Scripting (XSS) (CWE-79)

2026-01-21 disclosure@vulncheck.com

Moodle XSS

7.2

CVSS 3.1 · NVD

Severity by source

NVD PRIMARY

7.2 HIGH

AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Lifecycle Timeline

Analysis Generated

Mar 12, 2026 - 21:54 vuln.today

PoC Detected

Mar 05, 2026 - 19:45 vuln.today

Public exploit code

CVE Published

Jan 21, 2026 - 18:16 nvd

HIGH 7.2

DescriptionCVE.org

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.

AnalysisAI

Moodle 3.10.3 contains a persistent cross-site scripting vulnerability in the calendar event subtitle field that allows attackers to inject malicious scripts. [CVSS 7.2 HIGH]

Technical ContextAI

Classified as CWE-79 (Cross-site Scripting (XSS)). Affects Moodle. 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.

RemediationAI

Monitor vendor advisories for a patch. Implement output encoding and Content Security Policy headers. Restrict network access to the affected service where possible.