diff --git a/django/utils/html.py b/django/utils/html.py index df38c20519..a3a7238cba 100644 --- a/django/utils/html.py +++ b/django/utils/html.py @@ -6,6 +6,7 @@ import re from html.parser import HTMLParser from urllib.parse import parse_qsl, quote, unquote, urlencode, urlsplit, urlunsplit +from django.core.exceptions import SuspiciousOperation from django.utils.encoding import punycode from django.utils.functional import Promise, cached_property, keep_lazy, keep_lazy_text from django.utils.http import RFC3986_GENDELIMS, RFC3986_SUBDELIMS @@ -14,6 +15,7 @@ from django.utils.safestring import SafeData, SafeString, mark_safe from django.utils.text import normalize_newlines MAX_URL_LENGTH = 2048 +MAX_STRIP_TAGS_DEPTH = 50 @keep_lazy(SafeString) @@ -172,15 +174,19 @@ def _strip_once(value): @keep_lazy_text def strip_tags(value): """Return the given HTML with all tags stripped.""" - # Note: in typical case this loop executes _strip_once once. Loop condition - # is redundant, but helps to reduce number of executions of _strip_once. value = str(value) + # Note: in typical case this loop executes _strip_once twice (the second + # execution does not remove any more tags). + strip_tags_depth = 0 while "<" in value and ">" in value: + if strip_tags_depth >= MAX_STRIP_TAGS_DEPTH: + raise SuspiciousOperation new_value = _strip_once(value) if value.count("<") == new_value.count("<"): # _strip_once wasn't able to detect more tags. break value = new_value + strip_tags_depth += 1 return value diff --git a/docs/releases/4.2.17.txt b/docs/releases/4.2.17.txt index 5139d7034d..9db07f6da7 100644 --- a/docs/releases/4.2.17.txt +++ b/docs/releases/4.2.17.txt @@ -6,3 +6,19 @@ Django 4.2.17 release notes Django 4.2.17 fixes one security issue with severity "high" and one security issue with severity "moderate" in 4.2.16. + +CVE-2024-53907: Denial-of-service possibility in ``strip_tags()`` +================================================================= + +:func:`~django.utils.html.strip_tags` would be extremely slow to evaluate +certain inputs containing large sequences of nested incomplete HTML entities. +The ``strip_tags()`` method is used to implement the corresponding +:tfilter:`striptags` template filter, which was thus also vulnerable. + +``strip_tags()`` now has an upper limit of recursive calls to ``HTMLParser`` +before raising a :exc:`.SuspiciousOperation` exception. + +Remember that absolutely NO guarantee is provided about the results of +``strip_tags()`` being HTML safe. So NEVER mark safe the result of a +``strip_tags()`` call without escaping it first, for example with +:func:`django.utils.html.escape`. diff --git a/tests/utils_tests/test_html.py b/tests/utils_tests/test_html.py index 7ff5020fb6..579bb2a1e3 100644 --- a/tests/utils_tests/test_html.py +++ b/tests/utils_tests/test_html.py @@ -1,6 +1,7 @@ import os from datetime import datetime +from django.core.exceptions import SuspiciousOperation from django.core.serializers.json import DjangoJSONEncoder from django.test import SimpleTestCase from django.utils.functional import lazystr @@ -113,12 +114,18 @@ class TestUtilsHtml(SimpleTestCase): ("&h", "alert()h"), (">br>br>br>X", "XX"), + ("<" * 50 + "a>" * 50, ""), ) for value, output in items: with self.subTest(value=value, output=output): self.check_output(strip_tags, value, output) self.check_output(strip_tags, lazystr(value), output) + def test_strip_tags_suspicious_operation(self): + value = "<" * 51 + "a>" * 51, "" + with self.assertRaises(SuspiciousOperation): + strip_tags(value) + def test_strip_tags_files(self): # Test with more lengthy content (also catching performance regressions) for filename in ("strip_tags1.html", "strip_tags2.txt"):