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.
https://mail.python.org/archives/list/[email protected]/thread/5M7CGUW3XBRY7II4DK43KF7NQQ3TPZ6R/
https://github.com/python/cpython/pull/145987
https://github.com/python/cpython/issues/145986
https://github.com/python/cpython/commit/eb0e8be3a7e11b87d198a2c3af1ed0eccf532768
https://github.com/python/cpython/commit/e0a8a6da90597a924b300debe045cdb4628ee1f3
https://github.com/python/cpython/commit/196edfb06a7458377d4d0f4b3cd41724c1f3bd4a
Published: 2026-03-16
Updated: 2026-03-17
Base Score: 9
Vector: CVSS2#AV:N/AC:M/Au:N/C:C/I:C/A:P
Severity: High
Base Score: 7.8
Vector: CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Severity: High
Base Score: 6
Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Severity: Medium
EPSS: 0.00017