Inefficient Regular Expression Complexity

Summary

The fast-xml-parser is an open-source, pure JavaScript XML parser. The fast-xml-parser allows special characters in entity names, which are not escaped or sanitized. Since the entity name is used for creating a regex for searching and replacing entities in the XML body, an attacker can abuse it for Denial of Service (DoS) attacks. By crafting an entity name that results in an intentionally bad-performing regex and utilizing it in the entity replacement step of the parser, this can cause the parser to stall for an indefinite amount of time. This vulnerability affects fast-xml-parser versions prior to 4.2.4. Users are advised to upgrade. Users unable to upgrade should avoid using "DOCTYPE" parsing by setting the `processEntities: false` option.