Fix SSL client connection crash for SAN marked critical The patch for CVE-2013-4073 (https://gist.github.com/nahi/5880963) caused SSL crash when a SSL server returns the certificate that has critical SAN value. X509 extension could include 2 or 3 elements in it; [id, criticality, octet_string] if critical, [id, octet_string] if not. Making sure …

0001-Fix-SSL-client-connection-crash-for-SAN-marked-criti.patch

From 61c3537bd9f8e37b01a8e45644c489fd8696c94b Mon Sep 17 00:00:00 2001
From: Hiroshi Nakamura <[email protected]>
Date: Fri, 5 Jul 2013 23:22:29 +0900
Subject: [PATCH] Fix SSL client connection crash for SAN marked critical

The patch for CVE-2013-4073 caused SSL crash when a SSL server returns
the certificate that has critical SAN value.  X509 extension could
include 2 or 3 elements in it;

[id, criticality, octet_string] if critical,
[id, octet_string] if not.

Making sure to pick the last element of X509 extension and use it as SAN
value.
---
 ext/openssl/lib/openssl/ssl.rb |  2 +-
 test/openssl/test_ssl.rb       | 27 +++++++++++++++++----------
 2 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/ext/openssl/lib/openssl/ssl.rb b/ext/openssl/lib/openssl/ssl.rb
index 04eb592..741274a 100644
--- a/ext/openssl/lib/openssl/ssl.rb
+++ b/ext/openssl/lib/openssl/ssl.rb
@@ -98,7 +98,7 @@ module OpenSSL
       should_verify_common_name = true
       cert.extensions.each{|ext|
         next if ext.oid != "subjectAltName"
-        id, ostr = OpenSSL::ASN1.decode(ext.to_der).value
+        ostr = OpenSSL::ASN1.decode(ext.to_der).value.last
         sequence = OpenSSL::ASN1.decode(ostr.value)
         sequence.value.each{|san|
           case san.tag
diff --git a/test/openssl/test_ssl.rb b/test/openssl/test_ssl.rb
index daaaa0a..a3100a8 100644
--- a/test/openssl/test_ssl.rb
+++ b/test/openssl/test_ssl.rb
@@ -338,25 +338,32 @@ class OpenSSL::TestSSL < OpenSSL::SSLTestCase
   end
 
   def test_verify_certificate_identity
-    # creating NULL byte SAN certificate
+    [true, false].each do |criticality|
+      cert = create_null_byte_SAN_certificate(criticality)
+      assert_equal(false, OpenSSL::SSL.verify_certificate_identity(cert, 'www.example.com'))
+      assert_equal(true,  OpenSSL::SSL.verify_certificate_identity(cert, 'www.example.com\0.evil.com'))
+      assert_equal(false, OpenSSL::SSL.verify_certificate_identity(cert, '192.168.7.255'))
+      assert_equal(true,  OpenSSL::SSL.verify_certificate_identity(cert, '192.168.7.1'))
+      assert_equal(false, OpenSSL::SSL.verify_certificate_identity(cert, '13::17'))
+      assert_equal(true,  OpenSSL::SSL.verify_certificate_identity(cert, '13:0:0:0:0:0:0:17'))
+    end
+  end
+
+  # Create NULL byte SAN certificate
+  def create_null_byte_SAN_certificate(critical = false)
     ef = OpenSSL::X509::ExtensionFactory.new
     cert = OpenSSL::X509::Certificate.new
     cert.subject = OpenSSL::X509::Name.parse "/DC=some/DC=site/CN=Some Site"
-    ext = ef.create_ext('subjectAltName', 'DNS:placeholder,IP:192.168.7.1,IP:13::17')
+    ext = ef.create_ext('subjectAltName', 'DNS:placeholder,IP:192.168.7.1,IP:13::17', critical)
     ext_asn1 = OpenSSL::ASN1.decode(ext.to_der)
     san_list_der = ext_asn1.value.reduce(nil) { |memo,val| val.tag == 4 ? val.value : memo }
     san_list_asn1 = OpenSSL::ASN1.decode(san_list_der)
     san_list_asn1.value[0].value = 'www.example.com\0.evil.com'
-    ext_asn1.value[1].value = san_list_asn1.to_der
+    pos = critical ? 2 : 1
+    ext_asn1.value[pos].value = san_list_asn1.to_der
     real_ext = OpenSSL::X509::Extension.new ext_asn1
     cert.add_extension(real_ext)
-
-    assert_equal(false, OpenSSL::SSL.verify_certificate_identity(cert, 'www.example.com'))
-    assert_equal(true,  OpenSSL::SSL.verify_certificate_identity(cert, 'www.example.com\0.evil.com'))
-    assert_equal(false, OpenSSL::SSL.verify_certificate_identity(cert, '192.168.7.255'))
-    assert_equal(true,  OpenSSL::SSL.verify_certificate_identity(cert, '192.168.7.1'))
-    assert_equal(false, OpenSSL::SSL.verify_certificate_identity(cert, '13::17'))
-    assert_equal(true,  OpenSSL::SSL.verify_certificate_identity(cert, '13:0:0:0:0:0:0:17'))
+    cert
   end
 
   def test_tlsext_hostname
-- 
1.8.1.2

Using Array#last is very elegant. I came up with something much more complicated... Thanks, my friend, I'll commit the patch tonight! Do I need to inform someone when it's done, or will this simply be released with the next patch release?