Moodle 3.10.3 XSS in Calendar Event Subtitle
CVE-2021-47857 Published on January 21, 2026

Moodle 3.10.3 - 'label' Persistent Cross Site Scripting
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.

NVD

Vulnerability Analysis

CVE-2021-47857 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. Public availability of a proof of concept (POC) exploit exists for CVE-2021-47857. The potential impact of an exploit of this vulnerability is considered to have a small impact on confidentiality and integrity, and no impact on availability.

Attack Vector:
NETWORK
Attack Complexity:
LOW
Privileges Required:
NONE
User Interaction:
NONE
Scope:
CHANGED
Confidentiality Impact:
LOW
Integrity Impact:
LOW
Availability Impact:
NONE

Weakness Type

What is a XSS Vulnerability?

The software does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

CVE-2021-47857 has been classified to as a XSS vulnerability or weakness.


Products Associated with CVE-2021-47857

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Moodle
 

Affected Versions

Moodle Version 3.10.3 is affected by CVE-2021-47857

Exploit Probability

EPSS
0.03%
Percentile
8.97%

EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.