xmldom is a pure JavaScript W3C standard-based (XML DOM Level 2 Core) DOMParser and XMLSerializer module. Prior to @xmldom/xmldom versions 0.8.15 and 0.9.12, and in xmldom version 0.6.0 and earlier, the DOCUMENT_TYPE_NODE branch in lib/dom.js validates publicId, systemId, and internalSubset under requireWellFormed: true but emits DocumentType.name verbatim. A name containing > or whitespace can terminate the <!DOCTYPE ...> declaration and inject sibling markup; the value can be supplied through createDocumentType() on the 0.8.x and unscoped lines or through a direct DocumentType.name property write on every affected line. The default path and legacy creation-time behavior remain permissive, while the vulnerable strict path fails to enforce an XML Name. This issue is fixed in @xmldom/xmldom versions 0.8.15 and 0.9.12; no fixed version is available for xmldom.

Affected: npm: @xmldom/xmldom, npm: xmldom

## Summary

The `@xmldom/xmldom` serializer emits `DocumentType.name` verbatim into the `<!DOCTYPE …>` declaration with no well-formedness guard. GHSA-f6ww-3ggp-fr8h (CVE-2026-41674) hardened the serializer's `requireWellFormed` path for a DocumentType's sibling fields — `publicId`, `systemId`, and `internalSubset` — but it did **not** add any check for `name`. A `>` (or whitespace) in the name terminates the doctype declaration early, letting the remaining characters become sibling markup in the serialized output.

Because `requireWellFormed: true` — the recommended mitigation for the prior xmldom injection CVEs — performs no validation on the DocType `name`, this is a bypass of that control, in the same family as the open element-name (GHSA-w2rr-34g9-rvrj) and attribute-name (GHSA-4w3w-2rp5-g8jm) name-injection advisories.

## Details

The serializer's `DOCUMENT_TYPE_NODE` case runs the `requireWellFormed` block only against `publicId`, `systemId`, and `internalSubset`, then pushes `n.name` directly into the buffer between the `<!DOCTYPE ` prefix and the closing `>`:

- 0.9.x (v0.9.10, `bb7a085`): [serializer DocType case, `lib/dom.js#L3256-L3283`](https://github.com/xmldom/xmldom/blob/bb7a085dc5ba1eea3212388509b97bb4b4af32b9/lib/dom.js#L3256-L3283) — the `requireWellFormed` block ([#L3259-L3269](https://github.com/xmldom/xmldom/blob/bb7a085dc5ba1eea3212388509b97bb4b4af32b9/lib/dom.js#L3259-L3269)) validates `publicId`/`systemId`/`internalSubset` but not `name`, whic…

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Affected: Ubuntu:20.04:LTS: node-xmldom, Ubuntu:22.04:LTS: node-xmldom, Ubuntu:24.04:LTS: node-xmldom, Ubuntu:26.04:LTS: node-xmldom

xmldom is a pure JavaScript W3C standard-based (XML DOM Level 2 Core) DOMParser and XMLSerializer module. Prior to @xmldom/xmldom versions 0.8.15 and 0.9.12, and in xmldom version 0.6.0 and earlier, the DOCUMENT_TYPE_NODE branch in lib/dom.js validates publicId, systemId, and internalSubset under requireWellFormed: true but emits DocumentType.name verbatim. A name containing > or whitespace can terminate the <!DOCTYPE ...> declaration and inject sibling markup; the value can be supplied through createDocumentType() on the 0.8.x and unscoped lines or through a direct DocumentType.name property write on every affected line. The default path and legacy creation-time behavior remain permissive, while the vulnerable strict path fails to enforce an XML Name. This issue is fixed in @xmldom/xmldom versions 0.8.15 and 0.9.12; no fixed version is available for xmldom.