Prevent parsing non-standard-compliant JSON float values (Z#23245937 / PRT-021)

src/pretix/helpers/monkeypatching.py

@@ -251,6 +251,13 @@ def monkeypatch_csrf_middleware():
     BaseCsrfMiddleware._set_csrf_cookie = CsrfViewMiddleware._set_csrf_cookie
 
 
+def monkeypatch_json_constants():
+    from json.decoder import _CONSTANTS  # noqa
+    del _CONSTANTS['-Infinity']
+    del _CONSTANTS['Infinity']
+    del _CONSTANTS['NaN']
+
+
 def monkeypatch_all_at_ready():
     monkeypatch_vobject_performance()
     monkeypatch_pillow_safer()
@@ -259,3 +266,5 @@ def monkeypatch_all_at_ready():
     monkeypatch_cookie_morsel()
     monkeypatch_reportlab_imagereader()
     monkeypatch_csrf_middleware()
+    monkeypatch_json_constants()
+

src/tests/helpers/test_json.py

@@ -0,0 +1,39 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020  Raphael Michel and contributors
+# Copyright (C) 2020-today pretix GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+import json
+
+import pytest
+
+
+def test_allowed_json():
+    assert json.loads('{"float":1.5,"int":161,"arr":[]}') == {"float": 1.5, "int": 161, "arr": []}
+
+
+def test_disallowed_json_float_consts():
+    with pytest.raises(KeyError):
+        json.loads("Infinity")
+    with pytest.raises(KeyError):
+        json.loads("-Infinity")
+    with pytest.raises(KeyError):
+        json.loads("NaN")
+    with pytest.raises(KeyError):
+        json.loads("[123, NaN, Infinity, -Infinity]")