Fixed #17906 - Autoescaping {% cycle %} and {% firstof %} templatetags.

This commit adds "future" version of these two tags with auto-escaping
enabled.

django/template/defaulttags.py

@@ -5,13 +5,15 @@ import sys
 import re
 from datetime import datetime
 from itertools import groupby, cycle as itertools_cycle
+import warnings
 
 from django.conf import settings
 from django.template.base import (Node, NodeList, Template, Context, Library,
     TemplateSyntaxError, VariableDoesNotExist, InvalidTemplateLibrary,
     BLOCK_TAG_START, BLOCK_TAG_END, VARIABLE_TAG_START, VARIABLE_TAG_END,
     SINGLE_BRACE_START, SINGLE_BRACE_END, COMMENT_TAG_START, COMMENT_TAG_END,
-    VARIABLE_ATTRIBUTE_SEPARATOR, get_library, token_kwargs, kwarg_re)
+    VARIABLE_ATTRIBUTE_SEPARATOR, get_library, token_kwargs, kwarg_re,
+    _render_value_in_context)
 from django.template.smartif import IfParser, Literal
 from django.template.defaultfilters import date
 from django.utils.encoding import smart_text
@@ -54,15 +56,15 @@ class CsrfTokenNode(Node):
             # misconfiguration, so we raise a warning
             from django.conf import settings
             if settings.DEBUG:
-                import warnings
                 warnings.warn("A {% csrf_token %} was used in a template, but the context did not provide the value.  This is usually caused by not using RequestContext.")
             return ''
 
 class CycleNode(Node):
-    def __init__(self, cyclevars, variable_name=None, silent=False):
+    def __init__(self, cyclevars, variable_name=None, silent=False, escape=False):
         self.cyclevars = cyclevars
         self.variable_name = variable_name
         self.silent = silent
+        self.escape = escape        # only while the "future" version exists
 
     def render(self, context):
         if self not in context.render_context:
@@ -74,7 +76,9 @@ class CycleNode(Node):
             context[self.variable_name] = value
         if self.silent:
             return ''
-        return value
+        if not self.escape:
+            value = mark_safe(value)
+        return _render_value_in_context(value, context)
 
 class DebugNode(Node):
     def render(self, context):
@@ -97,14 +101,17 @@ class FilterNode(Node):
         return filtered
 
 class FirstOfNode(Node):
-    def __init__(self, vars):
+    def __init__(self, variables, escape=False):
-        self.vars = vars
+        self.vars = variables
+        self.escape = escape        # only while the "future" version exists
 
     def render(self, context):
         for var in self.vars:
             value = var.resolve(context, True)
             if value:
-                return smart_text(value)
+                if not self.escape:
+                    value = mark_safe(value)
+                return _render_value_in_context(value, context)
         return ''
 
 class ForNode(Node):
@@ -508,7 +515,7 @@ def comment(parser, token):
     return CommentNode()
 
 @register.tag
-def cycle(parser, token):
+def cycle(parser, token, escape=False):
     """
     Cycles among the given strings each time this tag is encountered.
 
@@ -541,6 +548,11 @@ def cycle(parser, token):
         {% endfor %}
 
     """
+    if not escape:
+        warnings.warn(
+            "'The syntax for the `cycle` template tag is changing. Load it "
+            "from the `future` tag library to start using the new behavior.",
+            PendingDeprecationWarning, stacklevel=2)
 
     # Note: This returns the exact same node on each {% cycle name %} call;
     # that is, the node object returned from {% cycle a b c as name %} and the
@@ -588,13 +600,13 @@ def cycle(parser, token):
     if as_form:
         name = args[-1]
         values = [parser.compile_filter(arg) for arg in args[1:-2]]
-        node = CycleNode(values, name, silent=silent)
+        node = CycleNode(values, name, silent=silent, escape=escape)
         if not hasattr(parser, '_namedCycleNodes'):
             parser._namedCycleNodes = {}
         parser._namedCycleNodes[name] = node
     else:
         values = [parser.compile_filter(arg) for arg in args[1:]]
-        node = CycleNode(values)
+        node = CycleNode(values, escape=escape)
     return node
 
 @register.tag
@@ -643,7 +655,7 @@ def do_filter(parser, token):
     return FilterNode(filter_expr, nodelist)
 
 @register.tag
-def firstof(parser, token):
+def firstof(parser, token, escape=False):
     """
     Outputs the first variable passed that is not False, without escaping.
 
@@ -657,11 +669,11 @@ def firstof(parser, token):
 
         {% if var1 %}
             {{ var1|safe }}
-        {% else %}{% if var2 %}
+        {% elif var2 %}
             {{ var2|safe }}
-        {% else %}{% if var3 %}
+        {% elif var3 %}
             {{ var3|safe }}
-        {% endif %}{% endif %}{% endif %}
+        {% endif %}
 
     but obviously much cleaner!
 
@@ -677,10 +689,16 @@ def firstof(parser, token):
         {% endfilter %}
 
     """
+    if not escape:
+        warnings.warn(
+            "'The syntax for the `firstof` template tag is changing. Load it "
+            "from the `future` tag library to start using the new behavior.",
+            PendingDeprecationWarning, stacklevel=2)
+
     bits = token.split_contents()[1:]
     if len(bits) < 1:
         raise TemplateSyntaxError("'firstof' statement requires at least one argument")
-    return FirstOfNode([parser.compile_filter(bit) for bit in bits])
+    return FirstOfNode([parser.compile_filter(bit) for bit in bits], escape=escape)
 
 @register.tag('for')
 def do_for(parser, token):

django/templatetags/future.py

@@ -1,14 +1,65 @@
 from django.template import Library
-from django.template.defaulttags import url as default_url, ssi as default_ssi
+from django.template import defaulttags
 
 register = Library()
 
+
 @register.tag
 def ssi(parser, token):
     # Used for deprecation path during 1.3/1.4, will be removed in 2.0
-    return default_ssi(parser, token)
+    return defaulttags.ssi(parser, token)
+
 
 @register.tag
 def url(parser, token):
     # Used for deprecation path during 1.3/1.4, will be removed in 2.0
-    return default_url(parser, token)
+    return defaulttags.url(parser, token)
+
+
+@register.tag
+def cycle(parser, token):
+    """
+    This is the future version of `cycle` with auto-escaping.
+
+    By default all strings are escaped.
+
+    If you want to disable auto-escaping of variables you can use:
+
+        {% autoescape off %}
+            {% cycle var1 var2 var3 as somecycle %}
+        {% autoescape %}
+
+    Or if only some variables should be escaped, you can use:
+
+        {% cycle var1 var2|safe var3|safe  as somecycle %}
+    """
+    return defaulttags.cycle(parser, token, escape=True)
+
+
+@register.tag
+def firstof(parser, token):
+    """
+    This is the future version of `firstof` with auto-escaping.
+
+    This is equivalent to:
+
+       {% if var1 %}
+           {{ var1 }}
+       {% elif var2 %}
+           {{ var2 }}
+       {% elif var3 %}
+           {{ var3 }}
+       {% endif %}
+
+    If you want to disable auto-escaping of variables you can use:
+
+        {% autoescape off %}
+            {% firstof var1 var2 var3 "<strong>fallback value</strong>" %}
+        {% autoescape %}
+
+    Or if only some variables should be escaped, you can use:
+
+        {% firstof var1 var2|safe var3 "<strong>fallback value</strong>"|safe %}
+
+    """
+    return defaulttags.firstof(parser, token, escape=True)

docs/internals/deprecation.txt

@@ -323,6 +323,10 @@ these changes.
 1.8
 ---
 
+* The :ttag:`cycle` and :ttag:`firstof` template tags will auto-escape their
+  arguments. In 1.6 and 1.7, this behavior is provided by the version of these
+  tags in the ``future`` template tag library.
+
 * The ``SEND_BROKEN_LINK_EMAILS`` setting will be removed. Add the
   :class:`django.middleware.common.BrokenLinkEmailsMiddleware` middleware to
   your :setting:`MIDDLEWARE_CLASSES` setting instead.

docs/ref/templates/builtins.txt

@@ -147,9 +147,8 @@ You can use any number of values in a ``{% cycle %}`` tag, separated by spaces.
 Values enclosed in single (``'``) or double quotes (``"``) are treated as
 string literals, while values without quotes are treated as template variables.
 
-Note that the variables included in the cycle will not be escaped.
+Note that currently the variables included in the cycle will not be escaped.
-This is because template tags do not escape their content. Any HTML or
+Any HTML or Javascript code contained in the printed variable will be rendered
-Javascript code contained in the printed variable will be rendered
 as-is, which could potentially lead to security issues.
 
 For backwards compatibility, the ``{% cycle %}`` tag supports the much inferior
@@ -190,6 +189,22 @@ call to ``{% cycle %}`` doesn't specify silent::
     {% cycle 'row1' 'row2' as rowcolors silent %}
     {% cycle rowcolors %}
 
+.. versionchanged:: 1.6
+
+To improve safety, future versions of ``cycle`` will automatically escape
+their output. You're encouraged to activate this behavior by loading
+``cycle`` from the ``future`` template library::
+
+    {% load cycle from future %}
+
+When using the ``future`` version, you can disable auto-escaping with::
+
+    {% for o in some_list %}
+        <tr class="{% autoescape off %}{% cycle rowvalue1 rowvalue2 %}{% endautoescape %}">
+            ...
+        </tr>
+    {% endfor %}
+
 .. templatetag:: debug
 
 debug
@@ -257,28 +272,44 @@ This is equivalent to::
 
     {% if var1 %}
         {{ var1|safe }}
-    {% else %}{% if var2 %}
+    {% elif var2 %}
         {{ var2|safe }}
-    {% else %}{% if var3 %}
+    {% elif var3 %}
         {{ var3|safe }}
-    {% endif %}{% endif %}{% endif %}
+    {% endif %}
 
 You can also use a literal string as a fallback value in case all
 passed variables are False::
 
     {% firstof var1 var2 var3 "fallback value" %}
 
-Note that the variables included in the firstof tag will not be
+Note that currently the variables included in the firstof tag will not be
-escaped. This is because template tags do not escape their content.
+escaped. Any HTML or Javascript code contained in the printed variable will be
-Any HTML or Javascript code contained in the printed variable will be
+rendered as-is, which could potentially lead to security issues. If you need
-rendered as-is, which could potentially lead to security issues. If you
+to escape the variables in the firstof tag, you must do so explicitly::
-need to escape the variables in the firstof tag, you must do so
-explicitly::
 
     {% filter force_escape %}
         {% firstof var1 var2 var3 "fallback value" %}
     {% endfilter %}
 
+.. versionchanged:: 1.6
+
+To improve safety, future versions of ``firstof`` will automatically escape
+their output. You're encouraged to activate this behavior by loading
+``firstof`` from the ``future`` template library::
+
+    {% load firstof from future %}
+
+When using the ``future`` version, you can disable auto-escaping with::
+
+    {% autoescape off %}
+        {% firstof var1 var2 var3 "<strong>fallback value</strong>" %}
+    {% endautoescape %}
+
+Or if only some variables should be escaped, you can use::
+
+    {% firstof var1 var2|safe var3 "<strong>fallback value</strong>"|safe %}
+
 .. templatetag:: for
 
 for

docs/releases/1.6.txt

@@ -160,6 +160,34 @@ Backwards incompatible changes in 1.6
 Features deprecated in 1.6
 ==========================
 
+Changes to :ttag:`cycle` and :ttag:`firstof`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The template system generally escapes all variables to avoid XSS attacks.
+However, due to an accident of history, the :ttag:`cycle` and :ttag:`firstof`
+tags render their arguments as-is.
+
+Django 1.6 starts a process to correct this inconsistency. The ``future``
+template library provides alternate implementations of :ttag:`cycle` and
+:ttag:`firstof` that autoescape their inputs. If you're using these tags,
+you're encourage to include the following line at the top of your templates to
+enable the new behavior::
+
+    {% load cycle from future %}
+
+or::
+
+    {% load firstof from future %}
+
+The tags implementing the old behavior have been deprecated, and in Django
+1.8, the old behavior will be replaced with the new behavior. To ensure
+compatibility with future versions of Django, existing templates should be
+modified to use the ``future`` versions.
+
+If necessary, you can temporarily disable auto-escaping with
+:func:`~django.utils.safestring.mark_safe` or :ttag:`{% autoescape off %}
+<autoescape>`.
+
 ``SEND_BROKEN_LINK_EMAILS`` setting
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

tests/regressiontests/templates/tests.py

@@ -773,6 +773,11 @@ class Templates(TestCase):
             'cycle23': ("{% for x in values %}{% cycle 'a' 'b' 'c' as abc silent %}{{ abc }}{{ x }}{% endfor %}", {'values': [1,2,3,4]}, "a1b2c3a4"),
             'included-cycle': ('{{ abc }}', {'abc': 'xxx'}, 'xxx'),
             'cycle24': ("{% for x in values %}{% cycle 'a' 'b' 'c' as abc silent %}{% include 'included-cycle' %}{% endfor %}", {'values': [1,2,3,4]}, "abca"),
+            'cycle25': ('{% cycle a as abc %}', {'a': '<'}, '<'),
+
+            'cycle26': ('{% load cycle from future %}{% cycle a b as ab %}{% cycle ab %}', {'a': '<', 'b': '>'}, '&lt;&gt;'),
+            'cycle27': ('{% load cycle from future %}{% autoescape off %}{% cycle a b as ab %}{% cycle ab %}{% endautoescape %}', {'a': '<', 'b': '>'}, '<>'),
+            'cycle28': ('{% load cycle from future %}{% cycle a|safe b as ab %}{% cycle ab %}', {'a': '<', 'b': '>'}, '<&gt;'),
 
             ### EXCEPTIONS ############################################################
 
@@ -804,7 +809,12 @@ class Templates(TestCase):
             'firstof07': ('{% firstof a b "c" %}', {'a':0}, 'c'),
             'firstof08': ('{% firstof a b "c and d" %}', {'a':0,'b':0}, 'c and d'),
             'firstof09': ('{% firstof %}', {}, template.TemplateSyntaxError),
-            'firstof10': ('{% firstof a %}', {'a': '<'}, '<'), # Variables are NOT auto-escaped.
+            'firstof10': ('{% firstof a %}', {'a': '<'}, '<'),
+
+            'firstof11': ('{% load firstof from future %}{% firstof a b %}', {'a': '<', 'b': '>'}, '&lt;'),
+            'firstof12': ('{% load firstof from future %}{% firstof a b %}', {'a': '', 'b': '>'}, '&gt;'),
+            'firstof13': ('{% load firstof from future %}{% autoescape off %}{% firstof a %}{% endautoescape %}', {'a': '<'}, '<'),
+            'firstof14': ('{% load firstof from future %}{% firstof a|safe b %}', {'a': '<'}, '<'),
 
             ### FOR TAG ###############################################################
             'for-tag01': ("{% for val in values %}{{ val }}{% endfor %}", {"values": [1, 2, 3]}, "123"),