Issue #17980: Fix possible abuse of ssl.match_hostname() for denial of service using certificates with many wildcards (CVE-2013-2099).

1 files changed, 8 insertions, 1 deletions

diff --git a/Lib/ssl.py b/Lib/ssl.py
index e901b640a6..90c21ceff7 100644
--- a/Lib/ssl.py
+++ b/Lib/ssl.py
@@ -108,9 +108,16 @@ 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.