@astrojs/rss: XML Injection via Unescaped RSS Feed Fields

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

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.

Source published

27 Jul 2026 19:54:23 UTC

Source modified

28 Jul 2026 14:27:56 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 4.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

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.

Source published

27 Jul 2026 21:17:05 UTC

Source modified

24 Oct 2026 13:10:00 UTC

Observed here

25 Oct 2026 14:19:22 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 4.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

## 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 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/[email protected]`.

Source published

20 Jul 2026 23:21:47 UTC

Source modified

12 Aug 2026 20:45:07 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

Publisher rating · MODERATE