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GHSA-8j5q-mfj2-5q9q
No affected components available
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(
`<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
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:
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:
enclosure: {
url: 'https://example.com/a.mp3',
length: 0,
type: 'audio/mpeg" /><link>https://evil.example.com</link><enclosure fake="',
}
// Result: RSS feed contains an injected <link> 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 <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.
Patches
Fixed in @astrojs/rss@4.0.19.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a low impact on the integrity of the data.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
Probability that this vulnerability will be exploited in the wild within the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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