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