CVE-2021-20280
MEDIUMCVE-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. O3 Security confirms whether CVE-2021-20280 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Cross-site scripting (XSS) and Server side request forgery (SSRF) in moodle
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 | 3.10.2 |
| 🐘Packagist | moodle/moodle | ≥ 3.9&&< 3.9.5 | 3.9.5 |
| 🐘Packagist | moodle/moodle | ≥ 3.8&&< 3.8.8 | 3.8.8 |
| 🐘Packagist | moodle/moodle | ≥ 3.5&&< 3.5.17 | 3.5.17 |
Research 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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2021-20280 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2021-20280. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-20280 in your dependencies?
O3 detects CVE-2021-20280 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.