CVE-2021-37700 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in @github/paste-markdown. 1 public exploit reference exists, so weaponization risk is real. O3 Security confirms whether CVE-2021-37700 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Clipboard-based DOM-XSS
Real-World Exposure
@github/paste-markdownReal-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
@github/paste-markdown is an npm package for pasting markdown objects. A self Cross-Site Scripting vulnerability exists in the @github/paste-markdown before version 0.3.4. If the clipboard data contains the string <table>, a div is dynamically created, and the clipboard content is copied into its innerHTML property without any sanitization, resulting in improper execution of JavaScript in the browser of the victim (the user who pasted the code). Users directed to copy text from a malicious website and paste it into pages that utilize this library are affected. This is fixed in version 0.3.4. Refer the to the referenced GitHub Advisory for more details including an example exploit.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @github/paste-markdown | all versions | 0.3.4 |
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 @github/paste-markdown. 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 @github/paste-markdown to 0.3.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-37700 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-2021-37700 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-2021-37700. 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-2021-37700 in your dependencies?
O3 detects CVE-2021-37700 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.