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Vulnerabilities
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CVE-2026-59728

Updated on 27 Jul 2026

Severity

4.3 Medium severity

Details

CVSS score
4.3
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
CWE ID
Links
NISTCIRCLRHELUbuntu

Overview

About vulnerability

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

item.source = parser.parse(
`&lt;source url="${result.source.url}"&gt;${result.source.title}&lt;/source&gt;`,
).source;

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

enclosure.type

item.enclosure = parser.parse(
`&lt;enclosure url="${enclosureURL}" length="${result.enclosure.length}" type="${result.enclosure.type}"/&gt;`,
).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:

source: {
url: 'https://legit.example.com',
title: '&lt;/source&gt;&lt;item&gt;&lt;title&gt;INJECTED&lt;/title&gt;&lt;link&gt;https://evil.com&lt;/link&gt;&lt;/item&gt;&lt;source&gt;',
}
// Result: RSS feed contains an injected &lt;item&gt; element with an evil.com link

enclosure.type injection:

enclosure: {
url: 'https://example.com/a.mp3',
length: 0,
type: 'audio/mpeg" /&gt;&lt;link&gt;https://evil.example.com&lt;/link&gt;&lt;enclosure fake="',
}
// Result: RSS feed contains an injected &lt;link&gt; element

Both injections were confirmed with fast-xml-parser: the injected "link": "https://evil.com" appears in the parsed output.

Impact

An attacker who can control source.title or enclosure.type values (e.g., via a CMS, database, or user-submitted content that populates RSSFeedItem) can inject arbitrary XML into the generated RSS feed. This corrupts feed structure, injects false metadata (e.g., a fake &lt;link&gt; 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.

Patches

Fixed in @astrojs/[email protected].

Details

Affected product:
astro
Affected packages:
@astrojs/underscore-redirects @ 2.10.15 (+48 more)

Fixes