GHSA-gpfj-4j6g-c4w9 is a medium-severity (CVSS 6.5) Cross-site Scripting (XSS) vulnerability in @github/paste-markdown. 1 public exploit reference exists, so weaponization risk is real. O3 Security confirms whether GHSA-gpfj-4j6g-c4w9 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Clipboard-based DOM-XSS
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.
@github/paste-markdownnpmDescription
Impact
A self Cross-Site Scripting vulnerability exists in the @github/paste-markdown library. 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.
The following @github/paste-markdown code snippet is triggered when the user pastes something and the browser's clipboard data contains an entry whose content-type is text/HTML.
function generateText(transfer: DataTransfer): string | undefined {
if (Array.from(transfer.types).indexOf('text/html') === -1) return
let html = transfer.getData('text/html')
if (!/<table/i.test(html)) return
html = html.replace(/<meta.*?>/, '')
const el = document.createElement('div')
el.innerHTML = html
const tables = el.querySelectorAll('table')
for (const table of tables) {
if (table.closest('[data-paste-markdown-skip]')) {
table.replaceWith(new Text(table.textContent || ''))
}
const formattedTable = tableMarkdown(table)
table.replaceWith(new Text(formattedTable))
}
return el.innerHTML
}
Patches
A security patch was released in version 0.3.4.
Workarounds
A Content Security Policy that prevents unsafe-inline helps reduce the likelihood of this vulnerability being exploited in modern browsers.
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 GHSA-gpfj-4j6g-c4w9 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 GHSA-gpfj-4j6g-c4w9 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 GHSA-gpfj-4j6g-c4w9. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-gpfj-4j6g-c4w9 in your dependencies?
O3 detects GHSA-gpfj-4j6g-c4w9 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.