Astro: XSS via Unescaped Attribute Names in Spread Props

published 2026-06-16 4 mo ago modified 2026-10-25 14 d ago also GHSA-jrpj-wcv7-9fh9 , EUVD-2026-38336

cvss: 4.2; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 13%
public exploits: 0; none known

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.

Patch / fix

fixed in 2

npm astro 6.4.6
astro astro 6.4.6

CISA SSVC

Exploitation: Proof of concept is public
Automatable: no
Technical impact: partial
Assessed: 4 mo ago (2026-06-23)

Exploit prediction

0.23% chance of exploitation in the next 30 days, higher than 13% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/withastro/astro/security/advisories/GHSA-jrpj-wcv7-9fh9 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	3.1	4.2	CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N
NVD	3.1	6.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
GitHub	3.1	4.2	CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
npm	astro	<6.4.6	6.4.6

Affected products

withastro astro

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

github.com /withastro/astro/security/advisories/GHSA-jrpj-wcv7-9fh9
exploit, web, vendor-advisory
nvd.nist.gov /vuln/detail/CVE-2026-54298
advisory
github.com /withastro/astro
package

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary