CVE-2026-59728: @astrojs/rss XML Injection Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-8j5q-mfj2-5q9q",
  "modified" : "2026-08-12T20:37:28Z",
  "published" : "2026-07-20T23:21:47Z",
  "aliases" : [ "CVE-2026-59728" ],
  "summary" : "@astrojs/rss: XML Injection via Unescaped RSS Feed Fields",
  "details" : "## Summary\n\nIn `@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.\n\n## Details\n\nTwo fields in `packages/astro-rss/src/index.ts` are affected:\n\n### `source.title`\n\n```typescript\nitem.source = parser.parse(\n  `<source url=\"${result.source.url}\">${result.source.title}</source>`,\n).source;\n```\n\n`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.\n\n### `enclosure.type`\n\n```typescript\nitem.enclosure = parser.parse(\n  `<enclosure url=\"${enclosureURL}\" length=\"${result.enclosure.length}\" type=\"${result.enclosure.type}\"/>`,\n).enclosure;\n```\n\n`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.\n\n## Proof of Concept\n\n`source.title` injection:\n\n```javascript\nsource: {\n  url: 'https://legit.example.com',\n  title: '</source><item><title>INJECTED</title><link>https://evil.com</link></item><source>',\n}\n// Result: RSS feed contains an injected <item> element with an evil.com link\n```\n\n`enclosure.type` injection:\n\n```javascript\nenclosure: {\n  url: 'https://example.com/a.mp3',\n  length: 0,\n  type: 'audio/mpeg\" /><link>https://evil.example.com</link><enclosure fake=\"',\n}\n// Result: RSS feed contains an injected <link> element\n```\n\nBoth injections were confirmed with `fast-xml-parser`: the injected `\"link\": \"https://evil.com\"` appears in the parsed output.\n\n## Impact\n\nAn 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.\n\n## Patches\n\nFixed in `@astrojs/rss@4.0.19`.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@astrojs/rss"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.0.0"
      }, {
        "fixed" : "4.0.19"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/withastro/astro/security/advisories/GHSA-8j5q-mfj2-5q9q"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-59728"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/withastro/astro/pull/17209"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/withastro/astro/commit/fbcfa039dfe3d700b239f595a6c55ee35e45bd06"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/withastro/astro"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/withastro/astro/releases/tag/@astrojs/rss@4.0.19"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-91" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-20T23:21:47Z",
    "nvd_published_at" : "2026-07-27T21:17:05Z"
  }
}