CVE-2021-47857Public exploitNetwork attack vectorHinoki check available

Stored script execution via unsanitized track label

Published Jan 21, 2026 · Updated Jan 21, 2026

Stored cross-site scripting in Moodle LMS 3.10.3 allows remote authenticated users to run script in another user's browser. The calendar event editor stores HTML in a media subtitle track's label attribute without neutralizing event-handler markup before rendering the event. An account permitted to create calendar events can plant the payload, and execution requires another user to view the saved event.

CVSS severity5.1
Medium
EPSS probability0.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Stored cross-site scripting in Moodle LMS 3.10.3 allows remote authenticated users to run script in another user's browser. The calendar event editor stores HTML in a media subtitle track's label attribute without neutralizing event-handler markup before rendering the event. An account permitted to create calendar events can plant the payload, and execution requires another user to view the saved event.

The record

CVE
CVE-2021-47857
Published
Jan 21, 2026
Updated
Jan 21, 2026
Vendor
Moodle
Product
Moodle LMS
Classifications
CWE-79, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 21, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 21, 2026Record 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=3.10.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Moodle · Moodle LMSversion=3.10.3

Published CVSS scores

7.2VulnCheck CNACVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
6.1NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
5.1VulnCheck CNACVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA: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.

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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 exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

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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