bpo-38945: UU Encoding: Don't let newline in filename corrupt the output format (#17418)

Author: stealthcopter

Lib/encodings/uu_codec.py

@@ -20,6 +20,10 @@ def uu_encode(input, errors='strict', filename='<data>', mode=0o666):
     read = infile.read
     write = outfile.write
 
+    # Remove newline chars from filename
+    filename = filename.replace('\n','\\n')
+    filename = filename.replace('\r','\\r')
+
     # Encode
     write(('begin %o %s\n' % (mode & 0o777, filename)).encode('ascii'))
     chunk = read(45)

Lib/test/test_uu.py

@@ -136,6 +136,15 @@ def test_garbage_padding(self):
                 decoded = codecs.decode(encodedtext, "uu_codec")
                 self.assertEqual(decoded, plaintext)
 
+    def test_newlines_escaped(self):
+        # Test newlines are escaped with uu.encode
+        inp = io.BytesIO(plaintext)
+        out = io.BytesIO()
+        filename = "test.txt\n\roverflow.txt"
+        safefilename = b"test.txt\\n\\roverflow.txt"
+        uu.encode(inp, out, filename)
+        self.assertIn(safefilename, out.getvalue())
+
 class UUStdIOTest(unittest.TestCase):
 
     def setUp(self):

Lib/uu.py

@@ -73,6 +73,13 @@ def encode(in_file, out_file, name=None, mode=None, *, backtick=False):
             name = '-'
         if mode is None:
             mode = 0o666
+
+        #
+        # Remove newline chars from name
+        #
+        name = name.replace('\n','\\n')
+        name = name.replace('\r','\\r')
+
         #
         # Write the data
         #

Misc/NEWS.d/next/Security/2019-12-01-22-44-40.bpo-38945.ztmNXc.rst

@@ -0,0 +1 @@
+Newline characters have been escaped when performing uu encoding to prevent them from overflowing into to content section of the encoded file. This prevents malicious or accidental modification of data during the decoding process.