--- a/Doc/library/ssl.rst

+++ b/Doc/library/ssl.rst

@@ -283,10 +283,10 @@ Certificate handling

    Verify that *cert* (in decoded format as returned by

    :meth:`SSLSocket.getpeercert`) matches the given *hostname*.  The rules

    applied are those for checking the identity of HTTPS servers as outlined

-   in :rfc:`2818`, except that IP addresses are not currently supported.

-   In addition to HTTPS, this function should be suitable for checking the

-   identity of servers in various SSL-based protocols such as FTPS, IMAPS,

-   POPS and others.

+   in :rfc:`2818` and :rfc:`6125`, except that IP addresses are not currently

+   supported. In addition to HTTPS, this function should be suitable for

+   checking the identity of servers in various SSL-based protocols such as

+   FTPS, IMAPS, POPS and others.

    :exc:`CertificateError` is raised on failure. On success, the function

    returns nothing::

@@ -301,6 +301,13 @@ Certificate handling

    .. versionadded:: 3.2

+   .. versionchanged:: 3.3.3

+      The function now follows :rfc:`6125`, section 6.4.3 and does neither

+      match multiple wildcards (e.g. ``*.*.com`` or ``*a*.example.org``) nor

+      a wildcard inside an internationalized domain names (IDN) fragment.

+      IDN A-labels such as ``www*.xn--pthon-kva.org`` are still supported,

+      but ``x*.python.org`` no longer matches ``xn--tda.python.org``.

+

 .. function:: cert_time_to_seconds(timestring)

    Returns a floating-point value containing a normal seconds-after-the-epoch

unchanged:

--- a/Lib/ssl.py

+++ b/Lib/ssl.py

@@ -129,25 +129,53 @@ class CertificateError(ValueError):

     pass

-def _dnsname_to_pat(dn, max_wildcards=1):

+def _dnsname_match(dn, hostname, max_wildcards=1):

+    """Matching according to RFC 6125, section 6.4.3

+

+    http://tools.ietf.org/html/rfc6125#section-6.4.3

+    """

     pats = []

-    for frag in dn.split(r'.'):

-        if frag.count('*') > max_wildcards:

-            # Issue #17980: avoid denials of service by refusing more

-            # than one wildcard per fragment.  A survery of established

-            # policy among SSL implementations showed it to be a

-            # reasonable choice.

-            raise CertificateError(

-                "too many wildcards in certificate DNS name: " + repr(dn))

-        if frag == '*':

-            # When '*' is a fragment by itself, it matches a non-empty dotless

-            # fragment.

-            pats.append('[^.]+')

-        else:

-            # Otherwise, '*' matches any dotless fragment.

-            frag = re.escape(frag)

-            pats.append(frag.replace(r'\*', '[^.]*'))

-    return re.compile(r'\A' + r'\.'.join(pats) + r'\Z', re.IGNORECASE)

+    if not dn:

+        return False

+

+    leftmost, *remainder = dn.split(r'.')

+

+    wildcards = leftmost.count('*')

+    if wildcards > max_wildcards:

+        # Issue #17980: avoid denials of service by refusing more

+        # than one wildcard per fragment.  A survery of established

+        # policy among SSL implementations showed it to be a

+        # reasonable choice.

+        raise CertificateError(

+            "too many wildcards in certificate DNS name: " + repr(dn))

+

+    # speed up common case w/o wildcards

+    if not wildcards:

+        return dn.lower() == hostname.lower()

+

+    # RFC 6125, section 6.4.3, subitem 1.

+    # The client SHOULD NOT attempt to match a presented identifier in which

+    # the wildcard character comprises a label other than the left-most label.

+    if leftmost == '*':

+        # When '*' is a fragment by itself, it matches a non-empty dotless

+        # fragment.

+        pats.append('[^.]+')

+    elif leftmost.startswith('xn--') or hostname.startswith('xn--'):

+        # RFC 6125, section 6.4.3, subitem 3.

+        # The client SHOULD NOT attempt to match a presented identifier

+        # where the wildcard character is embedded within an A-label or

+        # U-label of an internationalized domain name.

+        pats.append(re.escape(leftmost))

+    else:

+        # Otherwise, '*' matches any dotless string, e.g. www*

+        pats.append(re.escape(leftmost).replace(r'\*', '[^.]*'))

+

+    # add the remaining fragments, ignore any wildcards

+    for frag in remainder:

+        pats.append(re.escape(frag))

+

+    pat = re.compile(r'\A' + r'\.'.join(pats) + r'\Z', re.IGNORECASE)

+    return pat.match(hostname)

 def match_hostname(cert, hostname):

unchanged:

--- a/Lib/test/test_ssl.py

+++ b/Lib/test/test_ssl.py

@@ -304,11 +304,7 @@ class BasicSocketTests(unittest.TestCase

         fail(cert, 'Xa.com')

         fail(cert, '.a.com')

-        cert = {'subject': ((('commonName', 'a.*.com'),),)}

-        ok(cert, 'a.foo.com')

-        fail(cert, 'a..com')

-        fail(cert, 'a.com')

-

+        # only match one left-most wildcard

         cert = {'subject': ((('commonName', 'f*.com'),),)}

         ok(cert, 'foo.com')

         ok(cert, 'f.com')

@@ -323,6 +319,36 @@ class BasicSocketTests(unittest.TestCase

         fail(cert, 'example.org')

         fail(cert, 'null.python.org')

+        # error cases with wildcards

+        cert = {'subject': ((('commonName', '*.*.a.com'),),)}

+        fail(cert, 'bar.foo.a.com')

+        fail(cert, 'a.com')

+        fail(cert, 'Xa.com')

+        fail(cert, '.a.com')

+

+        cert = {'subject': ((('commonName', 'a.*.com'),),)}

+        fail(cert, 'a.foo.com')

+        fail(cert, 'a..com')

+        fail(cert, 'a.com')

+

+        # wildcard doesn't match IDNA prefix 'xn--'

+        idna = 'püthon.python.org'.encode("idna").decode("ascii")

+        cert = {'subject': ((('commonName', idna),),)}

+        ok(cert, idna)

+        cert = {'subject': ((('commonName', 'x*.python.org'),),)}

+        fail(cert, idna)

+        cert = {'subject': ((('commonName', 'xn--p*.python.org'),),)}

+        fail(cert, idna)

+

+        # wildcard in first fragment and  IDNA A-labels in sequent fragments

+        # are supported.

+        idna = 'www*.pythön.org'.encode("idna").decode("ascii")

+        cert = {'subject': ((('commonName', idna),),)}

+        ok(cert, 'www.pythön.org'.encode("idna").decode("ascii"))

+        ok(cert, 'www1.pythön.org'.encode("idna").decode("ascii"))

+        fail(cert, 'ftp.pythön.org'.encode("idna").decode("ascii"))

+        fail(cert, 'pythön.org'.encode("idna").decode("ascii"))

+

         # Slightly fake real-world example

         cert = {'notAfter': 'Jun 26 21:41:46 2011 GMT',

                 'subject': ((('commonName', 'linuxfrz.org'),),),

@@ -383,7 +409,7 @@ class BasicSocketTests(unittest.TestCase

         cert = {'subject': ((('commonName', 'a*b.com'),),)}

         ok(cert, 'axxb.com')

         cert = {'subject': ((('commonName', 'a*b.co*'),),)}

-        ok(cert, 'axxb.com')

+        fail(cert, 'axxb.com')

         cert = {'subject': ((('commonName', 'a*b*.com'),),)}

         with self.assertRaises(ssl.CertificateError) as cm:

             ssl.match_hostname(cert, 'axxbxxc.com')

--- a/Lib/ssl.py

+++ b/Lib/ssl.py

@@ -192,7 +192,7 @@ def match_hostname(cert, hostname):

     san = cert.get('subjectAltName', ())

     for key, value in san:

         if key == 'DNS':

-            if _dnsname_to_pat(value).match(hostname):

+            if _dnsname_match(value, hostname):

                 return

             dnsnames.append(value)

     if not dnsnames:

@@ -203,7 +203,7 @@ def match_hostname(cert, hostname):

                 # XXX according to RFC 2818, the most specific Common Name

                 # must be used.

                 if key == 'commonName':

-                    if _dnsname_to_pat(value).match(hostname):

+                    if _dnsname_match(value, hostname):

                         return

                     dnsnames.append(value)

     if len(dnsnames) > 1: