When an Expat parser with a registered ElementDeclHandler parses an inline document type definition containing a deeply nested content model a C stack overflow occurs.
Deployments are exposed when an Expat parser has an ElementDeclHandler registered and parses XML documents that can contain an inline document type definition. The stated impact is a C stack overflow causing high availability impact.
An attacker needs to supply or influence an XML document with an inline DTD whose content model is deeply nested. No user interaction is required, but the attacker must be able to reach parsing performed with a registered ElementDeclHandler.
Review Expat parser initialization for registration of an ElementDeclHandler, and identify whether that parser processes XML with inline document type definitions from untrusted or attacker-influenced sources. The provided information does not identify affected versions or a fixed version.