This vulnerability arises from the Expat XML parser used in CPython when parsing inline DTDs with deeply nested content models while an ElementDeclHandler is registered. The deeply nested structure causes a C stack overflow, classified under CWE-674 (Improper Control of a Resource Through a Reference to a Resource in Another Sphere). The CVSS 4.0 base score is 6.0, indicating medium severity, with network attack vector, low attack complexity, and partial privileges required. The vulnerability does not involve user interaction and affects confidentiality, integrity, and availability to a high degree.

Successful exploitation of this vulnerability can cause a C stack overflow, potentially leading to a denial of service by crashing the Python interpreter. The impact affects availability primarily, with high impact on confidentiality and integrity as per the CVSS vector, though no specific exploitation details are provided. There are no known active exploits in the wild at this time.

Patch status is not yet confirmed — check the Python Software Foundation's official advisories for current remediation guidance. Until a fix is available, users should avoid processing untrusted XML documents with deeply nested inline DTDs using Expat parsers with ElementDeclHandler registered. Monitor official Python channels for updates.