[Python-checkins] bpo-35603: Escape table header of make_table output that can cause potential XSS. (GH-11341)

[Serhiy Storchaka]

https://github.com/python/cpython/commit/78de01198b047347abc5e458851bb12c48429e24
commit: 78de01198b047347abc5e458851bb12c48429e24
branch: master
author: Xtreak <tir.karthi at gmail.com>
committer: Serhiy Storchaka <storchaka at gmail.com>
date: 2018-12-29T10:53:14+02:00
summary:

bpo-35603: Escape table header of make_table output that can cause potential XSS. (GH-11341)

files:
A Misc/NEWS.d/next/Library/2018-12-28-14-53-22.bpo-35603.rVCZAE.rst
M Lib/difflib.py
M Lib/test/test_difflib.py

diff --git a/Lib/difflib.py b/Lib/difflib.py
index 887c3c26cae4..4571817b9823 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -2036,6 +2036,10 @@ def make_table(self,fromlines,tolines,fromdesc='',todesc='',context=False,
                 s.append( fmt % (next_id[i],next_href[i],fromlist[i],
                                            next_href[i],tolist[i]))
         if fromdesc or todesc:
+            fromdesc = fromdesc.replace("&", "&").replace(">", ">") \
+                                                     .replace("<", "<")
+            todesc = todesc.replace("&", "&").replace(">", ">") \
+                                                 .replace("<", "<")
             header_row = '<thead><tr>%s%s%s%s</tr></thead>' % (
                 '<th class="diff_next"><br /></th>',
                 '<th colspan="2" class="diff_header">%s</th>' % fromdesc,
diff --git a/Lib/test/test_difflib.py b/Lib/test/test_difflib.py
index 745ccbd6659e..63ebdb0dc83b 100644
--- a/Lib/test/test_difflib.py
+++ b/Lib/test/test_difflib.py
@@ -238,6 +238,15 @@ def test_html_diff(self):
         with open(findfile('test_difflib_expect.html')) as fp:
             self.assertEqual(actual, fp.read())
 
+    def test_make_table_escape_table_header(self):
+        html_diff = difflib.HtmlDiff()
+        output = html_diff.make_table(patch914575_from1.splitlines(),
+                                      patch914575_to1.splitlines(),
+                                      fromdesc='<from>',
+                                      todesc='<to>')
+        self.assertIn('<from>', output)
+        self.assertIn('<to>', output)
+
     def test_recursion_limit(self):
         # Check if the problem described in patch #1413711 exists.
         limit = sys.getrecursionlimit()
diff --git a/Misc/NEWS.d/next/Library/2018-12-28-14-53-22.bpo-35603.rVCZAE.rst b/Misc/NEWS.d/next/Library/2018-12-28-14-53-22.bpo-35603.rVCZAE.rst
new file mode 100644
index 000000000000..03150c3aa494
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-12-28-14-53-22.bpo-35603.rVCZAE.rst
@@ -0,0 +1,2 @@
+Escape table header output of :meth:`difflib.HtmlDiff.make_table`.
+Patch by Karthikeyan Singaravelan.