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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-59728: 0.32% estimated exploitation activity in the next 30 days; percentile 25.30 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 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 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: enclosure.type injection: Both injections were confirmed with fast-xml-parser: the injected "link": "https://evil.com" appears in the…

Published by the source

20 Jul 2026, 23:21 UTC

Last modified by the source

12 Aug 2026, 20:45 UTC

Source last checked

26 Oct 2026, 13:01 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-8j5q-mfj2-5q9q

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-8j5q-mfj2-5q9q

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# Patch Next advisory brief: CVE-2026-59728

Advisory: @astrojs/rss: XML Injection via Unescaped RSS Feed Fields
IDs: CVE-2026-59728, GHSA-8j5q-mfj2-5q9q
Record: https://patchnext.com/advisories/cve-2026-59728 (revision 2, source checked 26 Oct 2026, 13:01 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @astrojs/rss 4.0.19. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @astrojs/rss: affected >= 1.0.0, < 4.0.19; fixed in 4.0.19

## Suggested inspection (read-only)
- `npm ls @astrojs/rss --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @astrojs/rss.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-8j5q-mfj2-5q9q (OSV record GHSA-8j5q-mfj2-5q9q lists affected ranges: npm @astrojs/rss >=1.0.0 <4.0.19 (fixed))
- Verified: https://github.com/advisories/GHSA-8j5q-mfj2-5q9q (GitHub-reviewed advisory GHSA-8j5q-mfj2-5q9q lists affected ranges: npm @astrojs/rss >=1.0.0 <4.0.19)

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