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. O3 Security confirms whether CVE-2020-7773 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Cross-site Scripting in markdown-it-highlightjs
Real-World Exposure
markdown-it-highlightjsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.
Description
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 | 3.3.1 |
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 markdown-it-highlightjs. 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 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
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-2020-7773 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-2020-7773. 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-2020-7773 in your dependencies?
O3 detects CVE-2020-7773 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.