[Security-announce][CVE-2026-4224] Stack overflow parsing XML with deeply nested DTD content models

There is a HIGH severity vulnerability affecting CPython.

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.

Please see the linked CVE ID for the latest information on affected versions:

• https://www.cve.org/CVERecord?id=CVE-2026-4224
• https://github.com/python/cpython/commit/eb0e8be3a7e11b87d198a2c3af1ed0eccf5...