A prototype pollution vulnerability exists in the function copy in dom.js in the xmldom (published as @xmldom/xmldom) package before 0.8.3 for Node.js via the p variable. NOTE: the vendor states "we are in the process of marking this report as invalid"; however, some third parties takes the position that "A prototype injection/Prototype pollution is not just when global objects are polluted with recursive merge or deep cloning but also when a target object is polluted."

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. Update to @xmldom/xmldom@~0.7.7, @xmldom/xmldom@~0.8.4 (dist-tag latest) or @xmldom/xmldom@>=0.9.0-beta.4 (dist-tag next). As a workaround, please one of the following approaches depending on your use case: instead of searching for elements in the whole DOM, only search in the documentElementor reject a document with a document that has more then 1 childNode.