Moodle
CVE-2021-47857
HIGH
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A05:2025 - Injection
ASVS 5.0
V1 - Encoding and Sanitization Output encoding, context-aware escaping
MITRE ATT&CK
2 techniques across 2 tactics: Initial Access, Execution The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Impact | CVSS 7.2 (HIGH). Attack vector: Network. Complexity: Low. Privileges required: None. User interaction: None. Public exploit/POC available. |
| Exploit ScenarioDerived | An attacker could exploit this vulnerability to inject malicious scripts. |
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Alert meAnalysisAIv1 – Mar 12, 2026
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]
RemediationAI
Monitor vendor advisories for a patch. Implement output encoding and Content Security Policy headers. Restrict network access to the affected service where possible.
Affects your stack
Find out whether the stacks and servers you run are on an affected version.
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
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.
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
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
Lifecycle Timeline
2DescriptionCVE.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.
Executive ViewAI
Organizations using Moodle 3.10.3 face moderate risk from CVE-2021-47857, a cross-site scripting vulnerability rated CVSS 7.2. Attackers could inject malicious scripts to steal user sessions, credentials, or perform actions on behalf of authenticated users. Proof-of-concept code is publicly available, increasing the risk of exploitation. Organizations should apply vendor updates when available and consider compensating controls in the interim.
Apply vendor patch. If immediate patching is not feasible: (1) Implement Content-Security-Policy headers; (2) Enable HttpOnly and SameSite cookie attributes; (3) Deploy WAF XSS/CSRF rules.
Threat Intelligence Overview
NVD
CVE.org
EPSS
Exploit-DB
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Cross-Site Scripting occurs when an application accepts untrusted data and sends it to a web browser without proper validation or encoding.
Affected Products (CPE)CVE.org
Moodle through 2.5.2 allows remote authenticated administrators to execute arbitrary programs by configuring the aspell
A command execution vulnerability exists in the default legacy spellchecker plugin in Moodle 3.10. Rated critical severi
A flaw was found in Moodle. Rated high severity (CVSS 8.1), this vulnerability is remotely exploitable, no authenticatio
In Moodle 2.x and 3.x, SQL injection can occur via user preferences. Rated critical severity (CVSS 9.8), this vulnerabil
The Moodle LMS Jmol plugin version 6.1 and earlier contains a path traversal vulnerability in jsmol.php. The query param
Multiple cross-site scripting (XSS) vulnerabilities in Moodle through 2.2.11, 2.3.x before 2.3.9, 2.4.x before 2.4.6, an
Unrestricted file upload vulnerability in the double extension support in the "image" module in Moodle 3.1.2 allows remo
Unrestricted file upload vulnerability in the "legacy course files" and "file manager" modules in Moodle 3.1.2 allows re
moodle before versions 3.5.2, 3.4.5, 3.3.8, 3.1.14 is vulnerable to an XML import of ddwtos could lead to intentional re
An issue was discovered in Moodle 3.x. Rated high severity (CVSS 8.8), this vulnerability is remotely exploitable, low a
Moodle 3.1.2 allows remote attackers to obtain sensitive information via unspecified vectors, related to a "SQL Injectio
Directory traversal vulnerability in repository/filesystem/lib.php in Moodle through 2.2.11, 2.3.x before 2.3.10, 2.4.x
GitHub PoC