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MEDIUM severity

CVE-2021-43558 — moodle

MEDIUM

CVE-2021-43558 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in moodle/moodle. A fix is available for moodle/moodle — see the affected versions and patch details below.

Cross-site Scripting in moodle

Also known asBIT-moodle-2021-43558GHSA-wpfp-q843-v772
Published
Updated
Affected
3 pkgs
Patched
3 / 3
Exploits
None indexed
Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
0.9%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs58th percentile — riskier than 58% of all scored CVEsHighest risk
0.00%0.46%0.92%1.37%0.3%0.9%Apr 26Aug 26Oct 26

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

How urgent is this, really

CVE-2021-43558 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

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 flaw was found in Moodle in versions 3.11 to 3.11.3, 3.10 to 3.10.7, 3.9 to 3.9.10 and earlier unsupported versions. A URL parameter in the filetype site administrator tool required extra sanitizing to prevent a reflected XSS risk.

Affected Packages

3 total 3 fixed
EcosystemPackageVulnerable rangeFix
🐘Packagistmoodle/moodle≥ 3.11.0&&< 3.11.43.11.4composer require moodle/moodle:^3.11.4
🐘Packagistmoodle/moodle≥ 3.10.0&&< 3.10.83.10.8composer require moodle/moodle:^3.10.8
🐘Packagistmoodle/moodle≥ 3.9.0&&< 3.9.113.9.11composer require moodle/moodle:^3.9.11

Affected Products

3 products · 6 configurations
Application
extra packages for enterprise linuxfedoraproject
1 version
7.0
OS
fedorafedoraproject
1 version
35
Application
moodlemoodle
≥ 3.11.0 && ≤ 3.8.8
range

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. Fix

    Update moodle/moodle to 3.11.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-43558 is resolved across your whole dependency graph.

  3. 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

A flaw was found in Moodle in versions 3.11 to 3.11.3, 3.10 to 3.10.7, 3.9 to 3.9.10 and earlier unsupported versions. A URL parameter in the filetype site administrator tool required extra sanitizing to prevent a reflected XSS risk.
O3 Security · Impact-Aware SCA

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CVE-2021-43558: moodle XSS — Fixed in 3.11.4