8000 [5.1.x] Fixed CVE-2025-32873 -- Mitigated potential DoS in strip_tags(). · django/django@0b42f6a · GitHub
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[5.1.x] Fixed CVE-2025-32873 -- Mitigated potential DoS in strip_tags().
Thanks to Elias Myllymäki for the report, and Shai Berger and Jake Howard for the reviews. Co-authored-by: Natalia <124304+nessita@users.noreply.github.com> Backport of 9f3419b from main.
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‎django/utils/html.py‎

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@@ -41,6 +41,9 @@
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MAX_STRIP_TAGS_DEPTH = 50
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# HTML tag that opens but has no closing ">" after 1k+ chars.
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long_open_tag_without_closing_re = _lazy_re_compile(r"<[a-zA-Z][^>]{1000,}")
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@keep_lazy(SafeString)
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def escape(text):
@@ -207,6 +210,9 @@ def _strip_once(value):
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def strip_tags(value):
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"""Return the given HTML with all tags stripped."""
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value = str(value)
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for long_open_tag in long_open_tag_without_closing_re.finditer(value):
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if long_open_tag.group().count("<") >= MAX_STRIP_TAGS_DEPTH:
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raise SuspiciousOperation
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# Note: in typical case this loop executes _strip_once twice (the second
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# execution does not remove any more tags).
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strip_tags_depth = 0

‎docs/releases/4.2.21.txt‎

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@@ -7,6 +7,17 @@ Django 4.2.21 release notes
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Django 4.2.21 fixes a security issue with severity "moderate", a data loss bug,
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and a regression in 4.2.20.
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CVE-2025-32873: Denial-of-service possibility in ``strip_tags()``
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=================================================================
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:func:`~django.utils.html.strip_tags` would be slow to evaluate certain inputs
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containing large sequences of incomplete HTML tags. This function is used to
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implement the :tfilter:`striptags` template filter, which was thus also
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vulnerable.
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:func:`~django.utils.html.strip_tags` now raises a :exc:`.SuspiciousOperation`
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exception if it encounters an unusually large number of unclosed opening tags.
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Bugfixes
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========
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‎docs/releases/5.1.9.txt‎

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@@ -7,6 +7,17 @@ Django 5.1.9 release notes
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Django 5.1.9 fixes a security issue with severity "moderate", a data loss bug,
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and a regression in 5.1.8.
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CVE-2025-32873: Denial-of-service possibility in ``strip_tags()``
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=================================================================
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:func:`~django.utils.html.strip_tags` would be slow to evaluate certain inputs
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containing large sequences of incomplete HTML tags. This function is used to
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implement the :tfilter:`striptags` template filter, which was thus also
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vulnerable.
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:func:`~django.utils.html.strip_tags` now raises a :exc:`.SuspiciousOperation`
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exception if it encounters an unusually large number of unclosed opening tags.
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Bugfixes
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========
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‎tests/utils_tests/test_html.py‎

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@@ -126,17 +126,30 @@ def test_strip_tags(self):
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("><!" + ("&" * 16000) + "D", "><!" + ("&" * 16000) + "D"),
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("X<<<<br>br>br>br>X", "XX"),
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("<" * 50 + "a>" * 50, ""),
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(">" + "<a" * 500 + "a", ">" + "<a" * 500 + "a"),
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("<a" * 49 + "a" * 951, "<a" * 49 + "a" * 951),
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("<" + "a" * 1_002, "<" + "a" * 1_002),
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)
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for value, output in items:
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with self.subTest(value=value, output=output):
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self.check_output(strip_tags, value, output)
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self.check_output(strip_tags, lazystr(value), output)
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def test_strip_tags_suspicious_operation(self):
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def test_strip_tags_suspicious_operation_max_depth(self):
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value = "<" * 51 + "a>" * 51, "<a>"
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with self.assertRaises(SuspiciousOperation):
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strip_tags(value)
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def test_strip_tags_suspicious_operation_large_open_tags(self):
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items = [
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">" + "<a" * 501,
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"<a" * 50 + "a" * 950,
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]
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for value in items:
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with self.subTest(value=value):
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with self.assertRaises(SuspiciousOperation):
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strip_tags(value)
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def test_strip_tags_files(self):
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# Test with more lengthy content (also catching performance regressions)
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for filename in ("strip_tags1.html", "strip_tags2.txt"):

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