CVE-2019-3847 is a medium-severity (CVSS 4.8) Cross-site Scripting (XSS) vulnerability in moodle/moodle. 2 public exploit or proof-of-concept references are indexed, so weaponization risk is real. A fix is available for moodle/moodle — see the affected versions and patch details below.
Moodle XSS Vulnerability
EPSS Exploitation Probability
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
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
A vulnerability was found in moodle before versions 3.6.3, 3.5.5, 3.4.8 and 3.1.17. Users with the "login as other users" capability (such as administrators/managers) can access other users' Dashboards, but the JavaScript those other users may have added to their Dashboard was not being escaped when being viewed by the user logging in on their behalf.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | moodle/moodle | ≥ 3.6.0&&< 3.6.3 | 3.6.3composer require moodle/moodle:^3.6.3 |
| 🐘Packagist | moodle/moodle | ≥ 3.5.0&&< 3.5.5 | 3.5.5composer require moodle/moodle:^3.5.5 |
| 🐘Packagist | moodle/moodle | ≥ 3.2.0&&< 3.4.8 | 3.4.8composer require moodle/moodle:^3.4.8 |
| 🐘Packagist | moodle/moodle | all versions | 3.1.17composer require moodle/moodle:^3.1.17 |
Affected Products
moodlemoodleResearch 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 3.6.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-3847 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-2019-3847 in your dependencies?
Find it across Packagist, including transitive dependencies.