CVE-2021-36398Network attack vector

Stored XSS via unsanitized user ID numbers

Published Mar 6, 2023 · Updated Mar 7, 2025

Stored XSS in Moodle LMS 3.11 allows remote authenticated users to execute script in another user's browser through a crafted user ID number. The web service token list renders the stored ID number without sufficient output sanitization, so HTML or script is interpreted when the list is viewed. An attacker must be able to set a crafted ID number, and another authenticated user must open the token list; the script then runs in that viewer's Moodle origin.

CVSS severity5.4
Medium
EPSS probability0.52%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in Moodle LMS 3.11 allows remote authenticated users to execute script in another user's browser through a crafted user ID number. The web service token list renders the stored ID number without sufficient output sanitization, so HTML or script is interpreted when the list is viewed. An attacker must be able to set a crafted ID number, and another authenticated user must open the token list; the script then runs in that viewer's Moodle origin.

The record

CVE
CVE-2021-36398
Published
Mar 6, 2023
Updated
Mar 7, 2025
Vendor
Moodle
Product
Moodle LMS
Classifications
CWE-79, T1189
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 6, 2023CVE publishedPublication date reported by the CVE source.
  2. Mar 7, 2025Record 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=3.11

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Moodle · Moodle LMSversion=3.11

Published CVSS scores

5.4CISA-ADPCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1189Drive-by Compromise

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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