Improper Input Validation

Summary

xmldom is a pure JavaScript W3C standard-based (XML DOM Level 2 Core) `DOMParser` and `XMLSerializer` module. xmldom parses XML that is not well-formed because it contains multiple top level elements, and adds all root nodes to the `childNodes` collection of the `Document`, without reporting any error or throwing. This breaks the assumption that there is only a single root node in the tree, which led to issuance of CVE-2022-39299 as it is a potential issue for dependents. This vulnerability affects @xmldom/xmldom versions prior to 0.7.7, 0.8.x prior to 0.8.4, 0.9.x prior to 0.9.0-beta4. It also affects all versions of xmldom. As a workaround, please follow one of the following approaches depending on your use case: instead of searching for elements in the whole DOM, only search in the `documentElement`or reject a document with a document that has more than 1 `childNode`.