Issue #17980: Fix possible abuse of ssl.match_hostname() for denial of service using...

diff --git a/Lib/ssl.py b/Lib/ssl.py
index 6ff5c5388420f149c8c9d9f8015c042654c883e6..30ee13b20700acb4796fa0cee231bb31f5c0d282 100644 (file)
--- a/Lib/ssl.py
+++ b/Lib/ssl.py
@@ -129,9 +129,16 @@ class CertificateError(ValueError):
     pass
 
 
-def _dnsname_to_pat(dn):
+def _dnsname_to_pat(dn, max_wildcards=1):
     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.

diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
index 815475ea4dd52ad0c29d3a7d6a6ffc550161863d..1c4aa7ca1e0ade92baaf9a5fb688f86499ee67ef 100644 (file)
--- a/Lib/test/test_ssl.py
+++ b/Lib/test/test_ssl.py
@@ -349,6 +349,17 @@ class BasicSocketTests(unittest.TestCase):
         self.assertRaises(ValueError, ssl.match_hostname, None, 'example.com')
         self.assertRaises(ValueError, ssl.match_hostname, {}, 'example.com')
 
+        # Issue #17980: avoid denials of service by refusing more than one
+        # wildcard per fragment.
+        cert = {'subject': ((('commonName', 'a*b.com'),),)}
+        ok(cert, 'axxb.com')
+        cert = {'subject': ((('commonName', 'a*b.co*'),),)}
+        ok(cert, 'axxb.com')
+        cert = {'subject': ((('commonName', 'a*b*.com'),),)}
+        with self.assertRaises(ssl.CertificateError) as cm:
+            ssl.match_hostname(cert, 'axxbxxc.com')
+        self.assertIn("too many wildcards", str(cm.exception))
+
     def test_server_side(self):
         # server_hostname doesn't work for server sockets
         ctx = ssl.SSLContext(ssl.PROTOCOL_SSLv23)

diff --git a/Misc/NEWS b/Misc/NEWS
index 14be9391d35d5c756e3debeb9328e8d111dd85a9..1a516b77396067ab7a324ab6a3dc79e324f40b90 100644 (file)
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -24,6 +24,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #17980: Fix possible abuse of ssl.match_hostname() for denial of
+  service using certificates with many wildcards (CVE-2013-2099).
+
 - Issue #17981: Closed socket on error in SysLogHandler.
 
 - Fix typos in the multiprocessing module.