How severe is CVE-2021-47857?

CVE-2021-47857 has a CVSS 3.x base score of 7.2, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2021-47857 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (23rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-47857?

CVE-2021-47857 affects Moodle. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-47857?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2021-47857 have an EU (EUVD) identifier?

Yes. CVE-2021-47857 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-3616.

When was CVE-2021-47857 published?

CVE-2021-47857 was published on 2026-01-21 and last updated on 2026-06-17.

CVE-2021-47857

CVE-2021-47857 is a high-severity vulnerability in Moodle with a CVSS 3.x base score of 7.2. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: High (CVSS 3.x base score 7.2)
CVSS v4: 5.1
EPSS exploit prediction: 0% (23rd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-3616
Weakness: CWE-79
Affected product: Moodle
Published: 2026-01-21
Last modified: 2026-06-17

Description

Moodle 3.10.3 contains a persistent cross-site scripting vulnerability in the calendar event subtitle field that allows attackers to inject malicious scripts. Attackers can craft a calendar event with malicious JavaScript in the subtitle track label to execute arbitrary code when users view the event.

Frequently asked questions

What is CVE-2021-47857?: Moodle 3.10.3 contains a persistent cross-site scripting vulnerability in the calendar event subtitle field that allows attackers to inject malicious scripts. Attackers can craft a calendar event with malicious JavaScript in the subtitle track label to execute arbitrary code when users view the event.
How severe is CVE-2021-47857?: CVE-2021-47857 has a CVSS 3.x base score of 7.2, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2021-47857 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (23rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-47857?: CVE-2021-47857 affects Moodle. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-47857?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2021-47857 have an EU (EUVD) identifier?: Yes. CVE-2021-47857 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-3616.
When was CVE-2021-47857 published?: CVE-2021-47857 was published on 2026-01-21 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:moodle:moodle:3.10.3:*:*:*:*:*:*:*

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