CVE-2020-7773 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in markdown-it-highlightjs. 1 public exploit reference exists, so weaponization risk is real. A fix is available for markdown-it-highlightjs — see the affected versions and patch details below.
Cross-site Scripting in markdown-it-highlightjs
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2020-7773 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
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.
markdown-it-highlightjsnpmDescription
This affects the package markdown-it-highlightjs before 3.3.1. It is possible insert malicious JavaScript as a value of lang in the markdown-it-highlightjs Inline code highlighting feature. const markdownItHighlightjs = require("markdown-it-highlightjs"); const md = require('markdown-it'); const reuslt_xss = md() .use(markdownItHighlightjs, { inline: true }) .render('console.log(42){.">js}'); console.log(reuslt_xss);
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | markdown-it-highlightjs | all versions | 3.3.1npm install markdown-it-highlightjs@3.3.1 |
Affected Products
markdown-it-highlightjsmarkdown-it-highlightjs_projectResearch 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 markdown-it-highlightjs, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update markdown-it-highlightjs to 3.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-7773 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-2020-7773 in your dependencies?
Find it across npm, including transitive dependencies.