BIT-python-2026-4224: Stack overflow parsing XML with deeply nested DTD content models

Published Mar 16, 2026

Updated

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.

Affected Software

1 affected component

Expat Expat

Event History

Mar 16, 2026

CVE Published

via OSV·05:52 PM

Data Sourced

via OSV·05:52 PM

DescriptionSeverity

Frequently Asked Questions

Which deployments are exposed to this issue?

Deployments are exposed when an Expat parser has an ElementDeclHandler registered and parses XML containing an inline document type definition with a deeply nested content model.

What must an attacker provide to trigger the failure?

The parser must process an inline DTD whose content model is deeply nested. The vulnerable condition also requires that an ElementDeclHandler is registered on the parser.

How can I determine whether my application is affected?

Review where Expat parsers are created to determine whether an ElementDeclHandler is registered. Also identify whether those parsers accept XML documents that can include inline DTDs and deeply nested content models.

BIT-python-2026-4224: Stack overflow parsing XML with deeply nested DTD content models

Affected Software

Event History

Frequently Asked Questions

Which deployments are exposed to this issue?

What must an attacker provide to trigger the failure?

How can I determine whether my application is affected?

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Frequently Asked Questions

Which deployments are exposed to this issue?

What must an attacker provide to trigger the failure?

How can I determine whether my application is affected?