{"id":"CVE-2026-59728","aliases":["GHSA-8j5q-mfj2-5q9q"],"url":"https://o3.security/vulnerability/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`.","published":"2026-07-27T19:54:23.009Z","modified":"2026-10-21T02:58:49.253239395Z","cvss":{"score":4.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N"},"epss":{"score":0.00265,"percentile":0.18247,"asOf":"2026-09-05"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"@astrojs/rss","fixedVersion":"4.0.19"}],"fix":{"url":"https://github.com/withastro/astro/commit/fbcfa039dfe3d700b239f595a6c55ee35e45bd06","label":"withastro/astro@fbcfa03"},"references":[{"type":"WEB","url":"https://github.com/withastro/astro/releases/tag/@astrojs/rss@4.0.19"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59728.json"},{"type":"ADVISORY","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":"FIX","url":"https://github.com/withastro/astro/commit/fbcfa039dfe3d700b239f595a6c55ee35e45bd06"},{"type":"FIX","url":"https://github.com/withastro/astro/pull/17209"},{"type":"PACKAGE","url":"https://github.com/withastro/astro"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:58:49.253239395Z"}}