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[3.10] gh-145986: Avoid unbound C recursion in conv_content_model in pyexpat.c (CVE 2026-4224) (GH-145987) #146002

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[3.10] gh-145986: Avoid unbound C recursion in conv_content_model in pyexpat.c (CVE 2026-4224) (GH-145987) #146002

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[3.10] gh-145986: Avoid unbound C recursion in `conv_content_model` i…
StanFromIreland Mar 15, 2026
d013b14
Update Misc/NEWS.d/next/Security/2026-03-14-17-31-39.gh-issue-145986.…
StanFromIreland Mar 15, 2026
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20 changes: 19 additions & 1 deletion Lib/test/test_pyexpat.py
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@
from xml.parsers import expat
from xml.parsers.expat import errors

from test.support import import_helper
from test.support import import_helper, infinite_recursion
from test.support import sortdict


Expand Down Expand Up @@ -648,6 +648,24 @@ def test_change_size_2(self):
parser.Parse(xml2, True)
self.assertEqual(self.n, 4)

class ElementDeclHandlerTest(unittest.TestCase):
def test_deeply_nested_content_model(self):
# This should raise a RecursionError and not crash.
# See https://github.com/python/cpython/issues/145986.
N = 500_000
data = (
b'<!DOCTYPE root [\n<!ELEMENT root '
+ b'(a, ' * N + b'a' + b')' * N
+ b'>\n]>\n<root/>\n'
)

parser = expat.ParserCreate()
parser.ElementDeclHandler = lambda _1, _2: None
with infinite_recursion():
with self.assertRaises(RecursionError):
parser.Parse(data)


class MalformedInputTest(unittest.TestCase):
def test1(self):
xml = b"\0\r\n"
Expand Down
4 changes: 4 additions & 0 deletions Misc/NEWS.d/next/Security/2026-03-14-17-31-39.gh-issue-145986.ifSSr8.rst
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@@ -0,0 +1,4 @@
:mod:`xml.parsers.expat`: Fixed a crash caused by unbounded C recursion when
converting deeply nested XML content models with
:meth:`~xml.parsers.expat.xmlparser.ElementDeclHandler`.
This addresses `CVE-2026-4224 <https://www.cve.org/CVERecord?id=CVE-2026-4224>`_.
8 changes: 7 additions & 1 deletion Modules/pyexpat.c
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Original file line number Diff line number Diff line change
Expand Up @@ -574,6 +574,10 @@ static PyObject *
conv_content_model(XML_Content * const model,
PyObject *(*conv_string)(const XML_Char *))
{
if (Py_EnterRecursiveCall(" in conv_content_model")) {
return NULL;
}

PyObject *result = NULL;
PyObject *children = PyTuple_New(model->numchildren);
int i;
Expand All @@ -585,14 +589,16 @@ conv_content_model(XML_Content * const model,
conv_string);
if (child == NULL) {
Py_XDECREF(children);
return NULL;
goto done;
}
PyTuple_SET_ITEM(children, i, child);
}
result = Py_BuildValue("(iiO&N)",
model->type, model->quant,
conv_string,model->name, children);
}
done:
Py_LeaveRecursiveCall();
return result;
}

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