From be5de958e9052e322b0087c6dba81cdad0c3e031 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Tue, 15 Jan 2019 15:03:36 -0800
Subject: [PATCH] bpo-35746: Fix segfault in ssl's cert parser (GH-11569)

Fix a NULL pointer deref in ssl module. The cert parser did not handle CRL
distribution points with empty DP or URI correctly. A malicious or buggy
certificate can result into segfault.

Signed-off-by: Christian Heimes <christian@python.org>

https://bugs.python.org/issue35746
(cherry picked from commit a37f52436f9aa4b9292878b72f3ff1480e2606c3)

Co-authored-by: Christian Heimes <christian@python.org>
---
 Lib/test/talos-2019-0758.pem                  | 22 +++++++++++++++++++
 Lib/test/test_ssl.py                          | 22 +++++++++++++++++++
 .../2019-01-15-18-16-05.bpo-35746.nMSd0j.rst  |  3 +++
 Modules/_ssl.c                                |  4 ++++
 4 files changed, 51 insertions(+)
 create mode 100644 Lib/test/talos-2019-0758.pem
 create mode 100644 Misc/NEWS.d/next/Security/2019-01-15-18-16-05.bpo-35746.nMSd0j.rst

diff --git a/Lib/test/talos-2019-0758.pem b/Lib/test/talos-2019-0758.pem
new file mode 100644
index 0000000000..13b95a77fd
--- /dev/null
+++ b/Lib/test/talos-2019-0758.pem
@@ -0,0 +1,22 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
index f1b9565c8d..b6794ce3a8 100644
--- a/Lib/test/test_ssl.py
+++ b/Lib/test/test_ssl.py
@@ -116,6 +116,7 @@ NONEXISTINGCERT = data_file("XXXnonexisting.pem")
 BADKEY = data_file("badkey.pem")
 NOKIACERT = data_file("nokia.pem")
 NULLBYTECERT = data_file("nullbytecert.pem")
+TALOS_INVALID_CRLDP = data_file("talos-2019-0758.pem")
 
 DHFILE = data_file("ffdh3072.pem")
 BYTES_DHFILE = os.fsencode(DHFILE)
@@ -365,6 +366,27 @@ class BasicSocketTests(unittest.TestCase):
         self.assertEqual(p['crlDistributionPoints'],
                          ('http://SVRIntl-G3-crl.verisign.com/SVRIntlG3.crl',))
 
+    def test_parse_cert_CVE_2019_5010(self):
+        p = ssl._ssl._test_decode_cert(TALOS_INVALID_CRLDP)
+        if support.verbose:
+            sys.stdout.write("\n" + pprint.pformat(p) + "\n")
+        self.assertEqual(
+            p,
+            {
+                'issuer': (
+                    (('countryName', 'UK'),), (('commonName', 'cody-ca'),)),
+                'notAfter': 'Jun 14 18:00:58 2028 GMT',
+                'notBefore': 'Jun 18 18:00:58 2018 GMT',
+                'serialNumber': '02',
+                'subject': ((('countryName', 'UK'),),
+                            (('commonName',
+                              'codenomicon-vm-2.test.lal.cisco.com'),)),
+                'subjectAltName': (
+                    ('DNS', 'codenomicon-vm-2.test.lal.cisco.com'),),
+                'version': 3
+            }
+        )
+
     def test_parse_cert_CVE_2013_4238(self):
         p = ssl._ssl._test_decode_cert(NULLBYTECERT)
         if support.verbose:
diff --git a/Misc/NEWS.d/next/Security/2019-01-15-18-16-05.bpo-35746.nMSd0j.rst b/Misc/NEWS.d/next/Security/2019-01-15-18-16-05.bpo-35746.nMSd0j.rst
new file mode 100644
index 0000000000..dffe347eec
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2019-01-15-18-16-05.bpo-35746.nMSd0j.rst
@@ -0,0 +1,3 @@
+[CVE-2019-5010] Fix a NULL pointer deref in ssl module. The cert parser did
+not handle CRL distribution points with empty DP or URI correctly. A
+malicious or buggy certificate can result into segfault.
diff --git a/Modules/_ssl.c b/Modules/_ssl.c
index 9894ad821d..9baec8a9bc 100644
--- a/Modules/_ssl.c
+++ b/Modules/_ssl.c
@@ -1516,6 +1516,10 @@ _get_crl_dp(X509 *certificate) {
         STACK_OF(GENERAL_NAME) *gns;
 
         dp = sk_DIST_POINT_value(dps, i);
+        if (dp->distpoint == NULL) {
+            /* Ignore empty DP value, CVE-2019-5010 */
+            continue;
+        }
         gns = dp->distpoint->name.fullname;
 
         for (j=0; j < sk_GENERAL_NAME_num(gns); j++) {
-- 
2.17.1

