CVE-2021-21366

### Impact xmldom versions 0.4.0 and older do not correctly preserve [system identifiers](https://www.w3.org/TR/2008/REC-xml-20081126/#d0e4313), [FPIs](https://en.wikipedia.org/wiki/Formal_Public_Identifier) or [namespaces](https://www.w3.org/TR/xml-names11/) when repeatedly parsing and serializing maliciously crafted documents. This may lead to unexpected syntactic changes during XML processing in some downstream applications. ### Patches Update to 0.5.0 (once it is released) ### Workarounds Downstream applications can validate the input and reject the maliciously crafted documents. ### References Similar to this one reported on the Go standard library: - https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilities/ ### For more information If you have any questions or comments about this advisory: * Open an issue in [`xmldom/xmldom`](https://github.com/xmldom/xmldom) * Email us: send an email to **all** addresses that are shown by `npm owner ls xmldom`