CVE-2021-36401

Stored XSS via unsanitized exported ID numbers

Published Mar 6, 2023 · Updated Mar 7, 2025

Stored XSS in Moodle LMS 3.11, 3.10 through 3.10.4, and 3.9 through 3.9.7 allows remote authenticated users to execute script. The export path writes user-controlled ID numbers into HTML-capable downloaded files without the additional sanitization needed to neutralize script markup. Exploitation requires a low-privileged account and a victim to export and open the file; script runs in the file's local origin, not the Moodle site's domain.

CVSS severity4.8
Medium
EPSS probability0.53%
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, 3.10 through 3.10.4, and 3.9 through 3.9.7 allows remote authenticated users to execute script. The export path writes user-controlled ID numbers into HTML-capable downloaded files without the additional sanitization needed to neutralize script markup. Exploitation requires a low-privileged account and a victim to export and open the file; script runs in the file's local origin, not the Moodle site's domain.

The record

CVE
CVE-2021-36401
Published
Mar 6, 2023
Updated
Mar 7, 2025
Vendor
Moodle
Product
Moodle LMS
Classifications
CWE-79, T1204.002
Attack vector
adjacent
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, 3.10 to 3.10.4, 3.9 to 3.9.7 and earlier unsupported versions

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesauthenticated

What is affected?

Moodle · Moodle LMSversion=3.11, 3.10 to 3.10.4, 3.9 to 3.9.7 and earlier unsupported versions

Published CVSS scores

4.8NIST NVDCVSS:3.1/AV:A/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
4.8CISA-ADPCVSS:3.1/AV:A/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)
Vectoradjacent
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1204.002User Execution: Malicious File

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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