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gh-146169: Prevent re-entrant Parse() calls in pyexpat #146179

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gh-146169: Prevent re-entrant Parse() calls in pyexpat #146179

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c924f57
gh-146174: Prevent re-entrant Parse() calls in pyexpat
okiemute04 Mar 19, 2026
0e67052
Add NEWS entry for pyexpat re-entrant fix
okiemute04 Mar 19, 2026
029e408
Add NEWS entry for pyexpat re-entrant fix
okiemute04 Mar 19, 2026
57faef4
Merge remote branch to resolve history divergence
okiemute04 Mar 19, 2026
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24 changes: 24 additions & 0 deletions Lib/test/test_pyexpat.py
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Original file line number Diff line number Diff line change
Expand Up @@ -276,6 +276,30 @@ def test_parse_again(self):
self.assertEqual(expat.ErrorString(cm.exception.code),
expat.errors.XML_ERROR_FINISHED)

def test_reentrant_parse_crash(self):
p = expat.ParserCreate(encoding="utf-16")

def start(name, attrs):
def handler(data):
p.Parse(data, 0)
p.CharacterDataHandler = handler

p.StartElementHandler = start
data = b"\xff\xfe<\x00a\x00>\x00x\x00"
with self.assertRaises(RuntimeError) as cm:
for i in range(len(data)):
p.Parse(data[i:i+1], i == len(data) - 1)
self.assertEqual(str(cm.exception),
"cannot call Parse() from within a handler")

def test_parse_normal(self):
p = expat.ParserCreate()
data = "<root><child/></root>".encode('utf-8')
try:
p.Parse(data, 1)
except RuntimeError:
self.fail("Parse() raised RuntimeError during normal operation")

class NamespaceSeparatorTest(unittest.TestCase):
def test_legal(self):
# Tests that make sure we get errors when the namespace_separator value
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-03-19-11-15-00.gh-issue-146169.manual.rst
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@@ -0,0 +1,3 @@
Prevent re-entrant calls to ``Parse()`` from within expat handlers,
which could cause a crash. Now raises :exc:`RuntimeError` when such a
call is attempted.
7 changes: 7 additions & 0 deletions Modules/pyexpat.c
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Original file line number Diff line number Diff line change
Expand Up @@ -857,6 +857,13 @@ pyexpat_xmlparser_Parse_impl(xmlparseobject *self, PyTypeObject *cls,
PyObject *data, int isfinal)
/*[clinic end generated code: output=8faffe07fe1f862a input=053e0f047e55c05a]*/
{

if (self->in_callback) {
PyErr_SetString(PyExc_RuntimeError,
"cannot call Parse() from within a handler");
return NULL;
}

const char *s;
Py_ssize_t slen;
Py_buffer view;
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