Reject non-numeric elements inside list coords

Tests/test_imagepath.py

@@ -51,6 +51,7 @@ def test_path() -> None:
         [0.0, 1.0],
         ((0, 1),),
         [(0, 1)],
+        [[0, 1]],
         ((0.0, 1.0),),
         [(0.0, 1.0)],
         array.array("f", [0, 1]),
@@ -68,6 +69,34 @@ def test_path_constructors(
     assert list(p) == [(0.0, 1.0)]
 
 
+@pytest.mark.parametrize(
+    "coords, expected",
+    (
+        ([[0, 1], [2, 3]], [(0.0, 1.0), (2.0, 3.0)]),
+        ([[0.0, 1.0], [2.0, 3.0]], [(0.0, 1.0), (2.0, 3.0)]),
+    ),
+)
+def test_path_list_of_lists(
+    coords: list[list[float]], expected: list[tuple[float, float]]
+) -> None:
+    p = ImagePath.Path(coords)
+    assert list(p) == expected
+
+
+@pytest.mark.parametrize(
+    "coords, message",
+    (
+        ([[1, 2, 3]], "coordinate list must contain exactly 2 coordinates"),
+        ([[1]], "coordinate list must contain exactly 2 coordinates"),
+        ([[[1, 2], [3, 4]]], "coordinate list must contain numbers"),
+        ([["a", "b"]], "coordinate list must contain numbers"),
+    ),
+)
+def test_invalid_list_coords(coords: list[list[object]], message: str) -> None:
+    with pytest.raises(ValueError, match=message):
+        ImagePath.Path(coords)
+
+
 def test_invalid_path_constructors() -> None:
     # Arrange / Act
     with pytest.raises(ValueError, match="incorrect coordinate type"):

docs/releasenotes/12.2.0.rst

@@ -33,6 +33,16 @@ Integer overflow when processing fonts
 If a font advances for each glyph by an exceeding large amount, when Pillow keeps track
 of the current position, it may lead to an integer overflow. This has been fixed.
 
+Heap buffer overflow with nested list coordinates
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Passing nested lists as coordinates to APIs that accept coordinates such as
+``ImagePath.Path``, :py:meth:`~PIL.ImageDraw.ImageDraw.polygon`
+and :py:meth:`~PIL.ImageDraw.ImageDraw.line` could cause a heap buffer overflow,
+as nested lists were recursively unpacked beyond the allocated buffer.
+Coordinate lists are now validated to contain exactly two numeric coordinates.
+This was introduced in Pillow 11.2.1.
+
 API changes
 ===========
 

src/path.c

@@ -118,14 +118,27 @@ assign_item_to_array(double *xy, Py_ssize_t j, PyObject *op) {
     } else if (PyNumber_Check(op)) {
         xy[j++] = PyFloat_AsDouble(op);
     } else if (PyList_Check(op)) {
+        if (PyList_GET_SIZE(op) != 2) {
+            PyErr_SetString(
+                PyExc_ValueError, "coordinate list must contain exactly 2 coordinates"
+            );
+            return -1;
+        }
         for (int k = 0; k < 2; k++) {
             PyObject *op1 = PyList_GetItemRef(op, k);
             if (op1 == NULL) {
                 return -1;
             }
-            j = assign_item_to_array(xy, j, op1);
+            if (PyFloat_Check(op1) || PyLong_Check(op1) || PyNumber_Check(op1)) {
+                j = assign_item_to_array(xy, j, op1);
+            } else {
+                j = -1;
+            }
             Py_DECREF(op1);
             if (j == -1) {
+                PyErr_SetString(
+                    PyExc_ValueError, "coordinate list must contain numbers"
+                );
                 return -1;
             }
         }