76 lines
2.9 KiB
Diff
76 lines
2.9 KiB
Diff
From 06fbba68024e0287b8e8f6da85ce840ffbfec3bc Mon Sep 17 00:00:00 2001
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From: Mikolaj Izdebski <mizdebsk@redhat.com>
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Date: Fri, 18 Dec 2020 16:08:43 +0100
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Subject: [PATCH 2/2] Fix CVE-2020-27783: mXSS due to the use of improper
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parser
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Backported from upstream commits 89e7aad6e7ff9ecd88678ff25f885988b184b26e
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and a105ab8dc262ec6735977c25c13f0bdfcdec72a7
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---
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src/lxml/html/clean.py | 25 +++++++++++++++++--------
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1 file changed, 17 insertions(+), 8 deletions(-)
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diff --git a/src/lxml/html/clean.py b/src/lxml/html/clean.py
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index da1f8706..c4fbfaa3 100644
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--- a/src/lxml/html/clean.py
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+++ b/src/lxml/html/clean.py
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@@ -61,12 +61,15 @@ __all__ = ['clean_html', 'clean', 'Cleaner', 'autolink', 'autolink_html',
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# This is an IE-specific construct you can have in a stylesheet to
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# run some Javascript:
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-_css_javascript_re = re.compile(
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- r'expression\s*\(.*?\)', re.S|re.I)
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+_replace_css_javascript = re.compile(
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+ r'expression\s*\(.*?\)', re.S|re.I).sub
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# Do I have to worry about @\nimport?
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-_css_import_re = re.compile(
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- r'@\s*import', re.I)
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+_replace_css_import = re.compile(
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+ r'@\s*import', re.I).sub
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+
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+_looks_like_tag_content = re.compile(
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+ r'</?[a-zA-Z]+|\son[a-zA-Z]+\s*=', re.ASCII).search
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# All kinds of schemes besides just javascript: that can cause
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# execution:
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@@ -292,8 +295,8 @@ class Cleaner(object):
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if not self.inline_style:
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for el in _find_styled_elements(doc):
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old = el.get('style')
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- new = _css_javascript_re.sub('', old)
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- new = _css_import_re.sub('', new)
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+ new = _replace_css_javascript('', old)
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+ new = _replace_css_import('', new)
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if self._has_sneaky_javascript(new):
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# Something tricky is going on...
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del el.attrib['style']
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@@ -305,9 +308,9 @@ class Cleaner(object):
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el.drop_tree()
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continue
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old = el.text or ''
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- new = _css_javascript_re.sub('', old)
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+ new = _replace_css_javascript('', old)
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# The imported CSS can do anything; we just can't allow:
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- new = _css_import_re.sub('', old)
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+ new = _replace_css_import('', new)
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if self._has_sneaky_javascript(new):
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# Something tricky is going on...
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el.text = '/* deleted */'
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@@ -522,6 +525,12 @@ class Cleaner(object):
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return True
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if 'expression(' in style:
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return True
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+ if '</noscript' in style:
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+ # e.g. '<noscript><style><a title="</noscript><img src=x onerror=alert(1)>">'
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+ return True
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+ if _looks_like_tag_content(style):
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+ # e.g. '<math><style><img src=x onerror=alert(1)></style></math>'
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+ return True
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return False
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def clean_html(self, html):
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--
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2.26.2
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