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56 lines
2.0 KiB
Python
56 lines
2.0 KiB
Python
# -*- coding: utf-8 -*-
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import json as json_
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import re
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import markupsafe
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JSON_SCRIPTSAFE_MAPPER = {
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'&': r'\u0026',
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'<': r'\u003c',
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'>': r'\u003e',
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'\u2028': r'\u2028',
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'\u2029': r'\u2029'
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}
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class _ScriptSafe(str):
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def __html__(self):
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# replacement can be done straight in the serialised JSON as the
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# problematic characters are not JSON metacharacters (and can thus
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# only occur in strings)
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return markupsafe.Markup(re.sub(
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r'[<>&\u2028\u2029]',
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lambda m: JSON_SCRIPTSAFE_MAPPER[m[0]],
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self,
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))
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class JSON:
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def loads(self, *args, **kwargs):
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return json_.loads(*args, **kwargs)
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def dumps(self, *args, **kwargs):
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""" JSON used as JS in HTML (script tags) is problematic: <script>
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tags are a special context which only waits for </script> but doesn't
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interpret anything else, this means standard htmlescaping does not
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work (it breaks double quotes, and e.g. `<` will become `<` *in
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the resulting JSON/JS* not just inside the page).
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However, failing to escape embedded json means the json strings could
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contains `</script>` and thus become XSS vector.
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The solution turns out to be very simple: use JSON-level unicode
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escapes for HTML-unsafe characters (e.g. "<" -> "\u003C". This removes
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the XSS issue without breaking the json, and there is no difference to
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the end result once it's been parsed back from JSON. So it will work
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properly even for HTML attributes or raw text.
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Also handle U+2028 and U+2029 the same way just in case as these are
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interpreted as newlines in javascript but not in JSON, which could
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lead to oddities and issues.
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.. warning::
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except inside <script> elements, this should be escaped following
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the normal rules of the containing format
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Cf https://code.djangoproject.com/ticket/17419#comment:27
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"""
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return _ScriptSafe(json_.dumps(*args, **kwargs))
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scriptsafe = JSON()
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