Persistent Cross-Site Scripting Vulnerability in Moodle by Moodle
CVE-2021-47857

5.1MEDIUM

Key Information:

Vendor

Moodle
Status
Moodle
Vendor
CVE Published:
21 January 2026

Badges

👾 Exploit Exists🟡 Public PoC

What is CVE-2021-47857?

Moodle version 3.10.3 is susceptible to a persistent cross-site scripting vulnerability in the calendar event subtitle field. This flaw permits malicious users to inject JavaScript code through crafted calendar events. When victim users view these events, the injected scripts can execute, potentially compromising user data and session integrity.

Affected Version(s)

Moodle 3.10.3

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

CVE-2021-47857 - Proof of Concept

References

https://www.exploit-db.com/exploits/49714
exploit
https://moodle.org/
product
https://www.vulncheck.com/advisories/moodle-label-persist...
third-party-advisory

CVSS V4

Score:
5.1
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
Low
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
Unknown

Timeline

  • 🟡

    Public PoC available

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

Credit

Vincent666 ibn Winnie
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