CVE-2026-59728

Astro is a web framework for content-driven websites. In versions 1.0.0 through 4.0.18, the source.title and enclosure.type item fields in packages/astro-rss/src/index.ts are interpolated directly into XML template strings without XML-character escaping before being parsed by fast-xml-parser. Both fields are validated only as z.string(), placing no restriction on XML special characters. An attacker who controls these values can inject arbitrary XML into the generated RSS feed: a value containing " can break out of an attribute (as with enclosure.type), and a value containing </source> can close an element early and inject additional nodes (as with source.title). This corrupts feed structure, injects false metadata (for example, a fake <link> pointing to a malicious URL), and can cause feed readers to misparse or display attacker-controlled content. In SSR mode (output: 'server'), the poisoned feed is served on every request to all subscribers. This issue has been fixed in version 4.0.19.

We have discovered 1,808 live websites that are affected by CVE-2026-59728.

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Affected Software

Product	Astro
Category	Static Site Generator
Vulnerable Domains	1,808 live websites (6.87% of Astro install base)
Vulnerable Versions	from 1 through 4.0.19
Vulnerable Versions Count	159 versions ( 34% of all versions)