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CVE-2021-20185

18
FAUCET Score

CVE-2021-20185 describes a denial-of-service vulnerability in Moodle versions prior to 3.10.1, 3.9.4, 3.8.7, and 3.5.16. The flaw allowed users to send messages without character limits, potentially causing client-side browser denial of service for recipients of excessively large messages. Rated with a CVSS score of 5.3 (Medium), this vulnerability has a low attack complexity and does not require user interaction or privileges, but its impact is limited to availability. The FAUCET Risk Score is 20/100, indicating a relatively low overall risk. There is no evidence of active exploitation, and no public exploit code (Metasploit, Nuclei, ExploitDB) is available. Community discussion and media coverage for this CVE are minimal, suggesting a low level of public awareness or concern.

Impacted Technologies

VendorProductVersion(s)CPE
>= 3.5.0, < 3.5.16CPE matchmatch criteria
cpe:2.3:a:moodle:moodle:*:*:*:*:*:*:*:*
>= 3.8.0, < 3.8.7CPE matchmatch criteria
cpe:2.3:a:moodle:moodle:*:*:*:*:*:*:*:*
>= 3.9.0, < 3.9.4CPE matchmatch criteria
cpe:2.3:a:moodle:moodle:*:*:*:*:*:*:*:*
3.10.0CPE matchmatch criteria
cpe:2.3:a:moodle:moodle:3.10.0:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

5.3MEDIUM

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
LOW
Exploitability Score
3.9
Impact Score
1.4
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.38%
Probability of exploitation in next 30 days
EPSS Percentile
69.2%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0138 is in the 50th percentile among its peer group of 23,725 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (4)

composerpatch availablevia ghsa
Product: moodle/moodleFixed in: 3.5.16
composerpatch availablevia ghsa
Product: moodle/moodleFixed in: 3.8.7
composerpatch availablevia ghsa
Product: moodle/moodleFixed in: 3.9.4
composerpatch availablevia ghsa
Product: moodle/moodleFixed in: 3.10.1

Vendor Advisories (1)

composerGHSA-c3j6-33r4-89q3medium

Moodle Client side denial of service via personal message

May 24, 2022

References

moodle.org / mod/forum/discuss.php
PatchVendor Advisory