CVE-2026-50146: Astro: Reflected XSS via unescaped slot name

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-06-22 · updated 2026-10-25
Weakness: CWE-80

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.

Affected products

withastro astro: before 6.3.3 — fixed in 6.3.3

How to fix

Upgrade to a fixed version: withastro astro 6.3.3. Check the vendor advisory for mitigations.

References

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

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