CVE-2021-20185Network attack vector

Browser denial of service via unbounded messages

Published Jan 28, 2021 · Updated Aug 3, 2024

Uncontrolled resource consumption in Moodle LMS allows remote attackers to deny recipients browser access with oversized personal messages. Personal messaging accepts and delivers unbounded message bodies without enforcing a character limit. The oversized body must reach a recipient, and the reported consequence is confined to client-side browser denial of service.

CVSS severity5.3
Medium
EPSS probability1.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uncontrolled resource consumption in Moodle LMS allows remote attackers to deny recipients browser access with oversized personal messages. Personal messaging accepts and delivers unbounded message bodies without enforcing a character limit. The oversized body must reach a recipient, and the reported consequence is confined to client-side browser denial of service.

The record

CVE
CVE-2021-20185
Published
Jan 28, 2021
Updated
Aug 3, 2024
Vendor
Moodle
Product
Moodle LMS
Classifications
CWE-770, CWE-400, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 28, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=moodle 3.10.1, moodle 3.9.4, moodle 3.8.7, moodle 3.5.16

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Moodle · Moodle LMSversion=moodle 3.10.1, moodle 3.9.4, moodle 3.8.7, moodle 3.5.16

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
CWE-400Uncontrolled Resource Consumption
T1499.003Application Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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