Astro: XSS via Unescaped Attribute Names in Spread Props

Astro is a web framework. Prior to 6.4.6, the spreadAttributes function in Astro's server-side rendering pipeline iterates over object keys and passes them directly to addAttribute, which interpolates the key into the HTML output without escaping. When a developer uses the spread syntax {...props} on an HTML element and the object keys come from an untrusted source (API, CMS, URL parameters), an attacker can inject arbitrary HTML attributes including event handlers like onmousemove, onclick, or break out of the attribute context entirely to inject new elements. This vulnerability is fixed in 6.4.6.

Source published

22 Jun 2026 17:33:15 UTC

Source modified

23 Jun 2026 16:11:01 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

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CVSS 3.1 · 4.2 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N