CVE-2021-20280 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in moodle/moodle. 1 public exploit reference exists, so weaponization risk is real. A fix is available for moodle/moodle — see the affected versions and patch details below.
Cross-site scripting (XSS) and Server side request forgery (SSRF) in moodle
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-20280 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
moodle/moodle🐘moodle/moodle🐘moodle/moodle🐘moodle/moodleReal-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
Text-based feedback answers required additional sanitizing to prevent stored XSS and blind SSRF risks in moodle before 3.10.2, 3.9.5, 3.8.8, 3.5.17.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | moodle/moodle | ≥ 3.10&&< 3.10.2 | 3.10.2composer require moodle/moodle:^3.10.2 |
| 🐘Packagist | moodle/moodle | ≥ 3.9&&< 3.9.5 | 3.9.5composer require moodle/moodle:^3.9.5 |
| 🐘Packagist | moodle/moodle | ≥ 3.8&&< 3.8.8 | 3.8.8composer require moodle/moodle:^3.8.8 |
| 🐘Packagist | moodle/moodle | ≥ 3.5&&< 3.5.17 | 3.5.17composer require moodle/moodle:^3.5.17 |
Affected Products
fedorafedoraprojectmoodlemoodleResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
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.
Fix
Update moodle/moodle to 3.10.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-20280 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2021-20280 in your dependencies?
Find it across Packagist, including transitive dependencies.