CVE-2021-21809

Name: CVE-2021-21809
Creator: NVD / NIST
Published: 2021-06-23T22:15:08.407+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.1/10EPSS 24.17%

Last modified Jun 17, 2026

CVE-2021-21809 is a critical-severity vulnerability rated 9.1/10 on the CVSS scale. A command execution vulnerability exists in the default legacy spellchecker plugin in Moodle 3.10. A specially crafted series of HTTP requests can lead to command execution. EPSS estimates a 24.17% chance of exploitation in the next 30 days.

Description

A command execution vulnerability exists in the default legacy spellchecker plugin in Moodle 3.10. A specially crafted series of HTTP requests can lead to command execution. An attacker must have administrator privileges to exploit this vulnerabilities.

Metrics

CVSS 3.1

9.1/10

CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

EPSS Probability

24.17%

97.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-78

Affected Software

Vendor	Product	Versions
Moodle	Moodle	3.10.0

References

http://packetstormsecurity.com/files/164481/Moodle-SpellChecker-Path-Authenticated-Remote-Command-Execution.htmlExploit, Third Party Advisory, VDB Entry
https://talosintelligence.com/vulnerability_reports/TALOS-2021-1277Exploit, Third Party Advisory
http://packetstormsecurity.com/files/164481/Moodle-SpellChecker-Path-Authenticated-Remote-Command-Execution.htmlExploit, Third Party Advisory, VDB Entry
https://talosintelligence.com/vulnerability_reports/TALOS-2021-1277Exploit, Third Party Advisory

Timeline

Published: Jun 23, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-21809?

How severe is CVE-2021-21809?

CVE-2021-21809 has a CVSS score of 9.1/10 (CRITICAL severity). The EPSS model estimates a 24.17% probability of exploitation in the next 30 days.

How do I fix CVE-2021-21809?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-21809?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST