{"id":"CVE-2026-59728","aliases":["GHSA-8j5q-mfj2-5q9q"],"title":"@astrojs/rss: XML Injection via Unescaped RSS Feed Fields","summary":"@astrojs/rss: XML Injection via Unescaped RSS Feed Fields","severity":"medium","cvss":4.3,"cwe":["CWE-91"],"vendor":"astrojs","product":"@astrojs/rss","ecosystem":"npm","affected":["@astrojs/rss >= 1.0.0, < 4.0.19"],"patched":["@astrojs/rss 4.0.19"],"published":"2026-07-20","updated":"2026-07-20","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-8j5q-mfj2-5q9q","references":[{"url":"https://github.com/withastro/astro/security/advisories/GHSA-8j5q-mfj2-5q9q"},{"url":"https://github.com/withastro/astro/pull/17209"},{"url":"https://github.com/withastro/astro/commit/fbcfa039dfe3d700b239f595a6c55ee35e45bd06"},{"url":"https://github.com/withastro/astro/releases/tag/@astrojs/rss@4.0.19"},{"url":"https://github.com/advisories/GHSA-8j5q-mfj2-5q9q"}],"tags":["ghsa","npm"],"ingestedAt":"2026-07-20T23:44:02.364Z","epss":0.00374,"epssPercentile":0.28507,"slug":"CVE-2026-59728","body":"## Overview\n\n## 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`.\n\n## Affected packages\n\n- `@astrojs/rss >= 1.0.0, < 4.0.19`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `@astrojs/rss 4.0.19`","depth":"sunlit","depthScore":24,"depthScoreParts":{"impact":23.7,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}