CVE-2021-27131Public exploitNetwork attack vector

Cross-site script execution via administrator HTML fields

Published May 16, 2023 · Updated Aug 3, 2024

Stored XSS in Moodle 3.10.1 allows remote authenticated users to execute scripts in visitors' browsers through Additional HTML. The Header and Footer settings in /admin/settings.php intentionally accept unsanitized JavaScript and render the saved content on every page. Only administrators can change these fields, and Moodle disputes the issue because site-specific JavaScript is intended; executed code can read browser-accessible cookies or alter page content.

CVSS severity5.4
Medium
EPSS probability0.69%
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 3.10.1 allows remote authenticated users to execute scripts in visitors' browsers through Additional HTML. The Header and Footer settings in /admin/settings.php intentionally accept unsanitized JavaScript and render the saved content on every page. Only administrators can change these fields, and Moodle disputes the issue because site-specific JavaScript is intended; executed code can read browser-accessible cookies or alter page content.

The record

CVE
CVE-2021-27131
Published
May 16, 2023
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. May 16, 2023CVE 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

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
Privilegesadmin
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

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

Public exploit references

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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