CVE-2026-50146 Astro: Reflected XSS via unescaped slot name
Attackers can inject arbitrary HTML via unescaped slot names in Astro components, leading to reflected XSS during server-side rendering.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-50146?
CVE-2026-50146 is a high-severity cross-site scripting vulnerability in withastro astro, published on 22 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Astro is a web framework. Prior to 6.3.3, 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 vulnerability is fixed in 6.3.3.
Weakness: CWE-80
Which versions are affected by CVE-2026-50146?
2 open source packages ship an affected version, including astro. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
astro npm | All versions | 6.3.3 |
astro npm | All versions | 6.3.3 |
Products include Astro Astro.
How do I fix CVE-2026-50146?
Upgrade astro to 6.3.3 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-50146 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-50146 exists.
Other vulnerabilities in withastro astro
- CVE-2024-56159 Server source code is exposed to the public if sourcemaps are enabled
- CVE-2026-54299 Astro: Host header SSRF in prerendered error page fetch
- CVE-2025-59837 astro allows bypass of image proxy domain validation leading to SSRF and potential XSS
- CVE-2025-64764 Astro is vulnerable to Reflected XSS via the server islands feature
- CVE-2025-64765 Astro middleware authentication checks based on url.pathname can be bypassed via url encoded values
Sources
Also known as CLSA-2026-1784943142, CLSA-2026-1784943144, CLSA-2026-1784943177, CLSA-2026-1792160953, CLSA-2026-1792161557, CLSA-2026-1792161558 and 6 more.