Description
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 products
python: python
References10
- github.com/python/cpython/commit/196edfb06a7458377d4d0f4b3cd417… Patch
- github.com/python/cpython/commit/642865ddf4b232da1f3b1f7abcfa32… Patch
- github.com/python/cpython/commit/af856a7177326ac25d9f66cc6dd28b… Patch
- github.com/python/cpython/commit/e0a8a6da90597a924b300debe045cd… Patch
- github.com/python/cpython/commit/eb0e8be3a7e11b87d198a2c3af1ed0… Patch
- github.com/python/cpython/pull/145987 Patch
- github.com/python/cpython/commit/24ce88b285f56ee11626cf5e472af3…
- github.com/python/cpython/issues/145986 Issue Tracking
- mail.python.org/archives/list/[email protected]/thre… Third Party Advisory
- www.openwall.com/lists/oss-security/2026/03/16/4 Mailing ListThird Party Advisory
Metrics
- CVSS 3.1
-
7.5
HIGH
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - CVSS 4.0
-
6.0
MEDIUM
Score source: CNA
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 1% percentile: 56 · as of 12 November 2026
- CWE
- CWE-674
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.