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CRITICAL severity

CVE-2021-21809 — moodle

CRITICAL

CVE-2021-21809 is a critical-severity (CVSS 9.1) OS Command Injection vulnerability in moodle/moodle. 3 public exploit or proof-of-concept references are indexed, so weaponization risk is real. The records list no fixed version yet; check the vendor advisory below and apply the mitigations in the meantime.

Moodle command execution vulnerability exists in the default legacy spellchecker plugin

Also known asBIT-moodle-2021-21809GHSA-c7jj-vfmr-j9mj
Published
Updated
Affected
3 pkgs
Patched
See advisory
Exploits
3 known
Exploitation data as of Nov 11, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
24.2%probability of exploitation in next 30 days
Moderate Risk0.00%
Lower risk than most CVEs98th percentile — riskier than 98% of all scored CVEsHighest risk
9.55%35.5%61.5%87.5%72.9%24.2%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

3 pkgs affected
🐘moodle/moodle🐘moodle/moodle🐘moodle/moodle

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

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

Affected Packages

3 total
EcosystemPackageVulnerable rangeFix
🐘Packagistmoodle/moodleall versionsNo fix
🐘Packagistmoodle/moodleall versionsNo fix
🐘Packagistmoodle/moodleall versionsNo fix

Affected Products

1 product · 1 configurations
Application
moodlemoodle
1 version
3.10.0
Exploits & PoCs
3

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

A command execution vulnerability exists in the default legacy spellchec…

talosintelligence.comNVDJun 2021

Report on github.com

github.comMetasploitSep 2021

Report on packetstormsecurity.com

packetstormsecurity.comNVDDec 2021

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for moodle/moodle, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Remediation status

    The records we use list no patched version of moodle/moodle for CVE-2021-21809. Check the maintainer's advisory, and where your build allows, override or pin the dependency away from the vulnerable range.

  3. Mitigate without a patch

    Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.

Frequently Asked Questions

A command execution vulnerability exists in the default legacy spellchecker plugin in a few Moodle multiple specific versions. A specially crafted series of HTTP requests can lead to command execution. An attacker must have administrator privileges to exploit this vulnerabilities.
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CVE-2021-21809: moodle (Critical 9.1)