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.
Weakness
The product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack.
Potential Mitigations
Related Attack Patterns
References
- https://github.com/python/cpython/commit/196edfb06a7458377d4d0f4b3cd41724c1f3bd4a
- https://github.com/python/cpython/commit/e0a8a6da90597a924b300debe045cdb4628ee1f3
- https://github.com/python/cpython/commit/eb0e8be3a7e11b87d198a2c3af1ed0eccf532768
- https://github.com/python/cpython/issues/145986
- https://github.com/python/cpython/pull/145987
- https://mail.python.org/archives/list/security-announce@python.org/thread/5M7CGUW3XBRY7II4DK43KF7NQQ3TPZ6R/
- http://www.openwall.com/lists/oss-security/2026/03/16/4