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EUVD-2026-342032

fkie_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.

GHSA-8j5q-mfj2-5q9q — @astrojs/rss: XML Injection via Unescaped RSS Feed Fields

Affected: npm: @astrojs/rss

## Summary

In `@astrojs/rss`, the `source.title` and `enclosure.type` item fields are interpolated directly into XML template strings without XML-character escaping before being parsed by `fast-xml-parser`. An attacker who controls these field values can inject arbitrary XML elements into the generated RSS feed.

## Details

Two fields in `packages/astro-rss/src/index.ts` are affected:

### `source.title`

```typescript item.source = parser.parse( `<source url="${result.source.url}">${result.source.title}</source>`, ).source; ```

`source.title` is validated only as `z.string()`, with no restriction on XML special characters. A value containing `</source>` followed by arbitrary XML is parsed as real XML elements, merging injected nodes into the RSS item.

### `enclosure.type`

```typescript item.enclosure = parser.parse( `<enclosure url="${enclosureURL}" length="${result.enclosure.length}" type="${result.enclosure.type}"/>`, ).enclosure; ```

`enclosure.type` is also `z.string()` and is interpolated into an XML attribute without escaping. A value containing `"` followed by additional XML can break out of the attribute and inject extra elements.

## Proof of Concept

`source.title` injection:

```javascript source: { url: 'https://legit.example.com', title: '</source><item><title>INJECTED</title><link>https://evil.com</link></item><source>', } // Result: RSS feed contains an injected <item> element with an evil.com link ```

`enclosure.type` injection:

```javascript…