From 506ba0df107f78c498d4487a833ef1d2d2bf6587 Mon Sep 17 00:00:00 2001
From: Christian Schneppe <christian@pix-art.de>
Date: Tue, 1 Aug 2017 12:20:15 +0200
Subject: workaround for OpenFire: check CN first in self signed certs

The self signed certificates created by OpenFire (Not sure if other
certs are affected as well) will crash the Java/Android TLS stack when
accessing getSubjectAlternativeNames() on the the peer certificate.

This usually goes unnoticed in other applications since the
DefaultHostnameVerifier checkes the CN first. That however is a
violation of RFC6125 section 6.4.4 which requires us to check for the
existence of SAN first.

This commit adds a work around where in self signed certificates we
check for the CN first as well. (Avoiding the call to
getSubjectAlternativeNames())
---
 .../messenger/crypto/XmppDomainVerifier.java       | 37 +++++++++++++++++++---
 1 file changed, 32 insertions(+), 5 deletions(-)

(limited to 'src/main/java/de/pixart/messenger/crypto/XmppDomainVerifier.java')

diff --git a/src/main/java/de/pixart/messenger/crypto/XmppDomainVerifier.java b/src/main/java/de/pixart/messenger/crypto/XmppDomainVerifier.java
index 26aa268e4..a894dbc1b 100644
--- a/src/main/java/de/pixart/messenger/crypto/XmppDomainVerifier.java
+++ b/src/main/java/de/pixart/messenger/crypto/XmppDomainVerifier.java
@@ -16,6 +16,7 @@ import org.bouncycastle.cert.jcajce.JcaX509CertificateHolder;
 
 import java.io.IOException;
 import java.security.cert.Certificate;
+import java.security.cert.CertificateEncodingException;
 import java.security.cert.X509Certificate;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -40,6 +41,13 @@ public class XmppDomainVerifier implements DomainHostnameVerifier {
                 return false;
             }
             X509Certificate certificate = (X509Certificate) chain[0];
+            if (isSelfSigned(certificate)) {
+                List<String> domains = getCommonNames(certificate);
+                if (domains.size() == 1 && domains.get(0).equals(domain)) {
+                    Log.d(LOGTAG, "accepted CN in cert self signed cert for " + domain);
+                    return true;
+                }
+            }
             Collection<List<?>> alternativeNames = certificate.getSubjectAlternativeNames();
             List<String> xmppAddrs = new ArrayList<>();
             List<String> srvNames = new ArrayList<>();
@@ -70,11 +78,7 @@ public class XmppDomainVerifier implements DomainHostnameVerifier {
                 }
             }
             if (srvNames.size() == 0 && xmppAddrs.size() == 0 && domains.size() == 0) {
-                X500Name x500name = new JcaX509CertificateHolder(certificate).getSubject();
-                RDN[] rdns = x500name.getRDNs(BCStyle.CN);
-                for (int i = 0; i < rdns.length; ++i) {
-                    domains.add(IETFUtils.valueToString(x500name.getRDNs(BCStyle.CN)[i].getFirst().getValue()));
-                }
+                domains.addAll(domains);
             }
             Log.d(LOGTAG, "searching for " + domain + " in srvNames: " + srvNames + " xmppAddrs: " + xmppAddrs + " domains:" + domains);
             if (hostname != null) {
@@ -89,6 +93,20 @@ public class XmppDomainVerifier implements DomainHostnameVerifier {
         }
     }
 
+    private static List<String> getCommonNames(X509Certificate certificate) {
+        List<String> domains = new ArrayList<>();
+        try {
+            X500Name x500name = new JcaX509CertificateHolder(certificate).getSubject();
+            RDN[] rdns = x500name.getRDNs(BCStyle.CN);
+            for (int i = 0; i < rdns.length; ++i) {
+                domains.add(IETFUtils.valueToString(x500name.getRDNs(BCStyle.CN)[i].getFirst().getValue()));
+            }
+            return domains;
+        } catch (CertificateEncodingException e) {
+            return domains;
+        }
+    }
+
     private static Pair<String, String> parseOtherName(byte[] otherName) {
         try {
             ASN1Primitive asn1Primitive = ASN1Primitive.fromByteArray(otherName);
@@ -132,6 +150,15 @@ public class XmppDomainVerifier implements DomainHostnameVerifier {
         return false;
     }
 
+    private boolean isSelfSigned(X509Certificate certificate) {
+        try {
+            certificate.verify(certificate.getPublicKey());
+            return true;
+        } catch (Exception e) {
+            return false;
+        }
+    }
+
     @Override
     public boolean verify(String domain, SSLSession sslSession) {
         return verify(domain, null, sslSession);
-- 
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