5.3

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2021-20185

CVE-2021-20185: Moodle Client side denial of service via personal message

It was found in Moodle before version 3.10.1, 3.9.4, 3.8.7 and 3.5.16 that messaging did not impose a character limit when sending messages, which could result in client-side (browser) denial of service for users receiving very large messages.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2021-20185

CVE-2021-20185:

5.3

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
moodle/moodle	composer	>= 3.5, < 3.5.16	3.5.16
moodle/moodle	composer	>= 3.8, < 3.8.7	3.8.7
moodle/moodle	composer	>= 3.9, < 3.9.4	3.9.4
moodle/moodle	composer	>= 3.10, < 3.10.1	3.10.1

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability stems from missing message size validation in the messaging subsystem. The core messaging function message_send() in message/lib.php is directly responsible for processing and delivering messages. In vulnerable versions, this function lacked input size checks, enabling transmission of unbounded message payloads. The CWE-400/770 mapping confirms this is a resource consumption issue, and the Moodle security advisory (MDL-67782) specifically references messaging component changes. While exact commit details are unavailable, message_send() is the logical entry point where size validation would be implemented, making it the most likely vulnerable function.

Vulnerable functions

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Vulnerability Intelligence
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WAF Protection Rules

WAF Rule

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Reasoning

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