CVE-2021-33040 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in epubjs. A fix is available for epubjs — see the affected versions and patch details below.
Cross-site Scripting in epubjs
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-33040 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,987 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
epubjsnpmDescription
managers/views/iframe.js in FuturePress EPub.js before 0.3.89 allows XSS.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | epubjs | all versions | 0.3.89npm install epubjs@0.3.89 |
Affected Products
epub.jsfuturepressDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for epubjs, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update epubjs to 0.3.89 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-33040 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-2021-33040 in your dependencies?
Find it across npm, including transitive dependencies.