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.
CVE-2021-47857
HIGHNVD 6.17.2▲Elevated
EchelonGraph scoreMEDIUM confidence
Score 7.2 from GitHub Security Advisory published 2026-01-21. NVD baseline CVSS 6.1; sources differ by 1.1.
Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
7.2EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
- Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 6.1Exploit: Elevated riskExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 6.1
- EG Score
- 7.2(medium)
- EG Risk
- 48(Track)EG Risk 48/100SSVC: Track
EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).
How it’s computedSeverity72% × 45%Exploitation40% × 40%Automatability0% × 15%Action: Routine — remediate on your standard cadence. - EPSS PROB
- 0%
- EPSS %ILE
- 31%
- KEV
- Not listed
Published
January 21, 2026
Last Modified
June 17, 2026
References (3)
- disclosure@vulncheckhttps://moodle.org/
- disclosure@vulncheckhttps://www.exploit-db.com/exploits/49714
- disclosure@vulncheckhttps://www.vulncheck.com/advisories/moodle-label-persistent-cross-site-scripting
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Frequently asked(5)
What is CVE-2021-47857?
CVE-2021-47857 is a high vulnerability published on January 21, 2026. 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…
When was CVE-2021-47857 disclosed?
CVE-2021-47857 was first published in the National Vulnerability Database on January 21, 2026, with the most recent update on June 17, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-47857 actively exploited?
CVE-2021-47857 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 69.3% of all scored CVEs.
What is the CVSS score of CVE-2021-47857?
CVE-2021-47857 has a CVSS v3 base score of 6.1 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 7.2.
How do I remediate CVE-2021-47857?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-47857, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.
Dependency Blast Radius
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