Use generated certificates in unit tests (#6346)

* Use generated certificates in unit tests
* Strict to ascii lowercase implementation

Co-authored-by: Jesse Wilson <jwilson@squareup.com>

okhttp/src/main/kotlin/okhttp3/internal/tls/OkHostnameVerifier.kt

@@ -16,14 +16,15 @@
  */
 package okhttp3.internal.tls
 
+import okhttp3.internal.canParseAsIpAddress
+import okhttp3.internal.toCanonicalHost
+import okio.utf8Size
 import java.security.cert.CertificateParsingException
 import java.security.cert.X509Certificate
 import java.util.Locale
 import javax.net.ssl.HostnameVerifier
 import javax.net.ssl.SSLException
 import javax.net.ssl.SSLSession
-import okhttp3.internal.canParseAsIpAddress
-import okhttp3.internal.toCanonicalHost
 
 /**
  * A HostnameVerifier consistent with [RFC 2818][rfc_2818].
@@ -61,12 +62,24 @@ object OkHostnameVerifier : HostnameVerifier {
 
   /** Returns true if [certificate] matches [hostname]. */
   private fun verifyHostname(hostname: String, certificate: X509Certificate): Boolean {
-    val hostname = hostname.toLowerCase(Locale.US)
+    val hostname = hostname.asciiToLowercase()
     return getSubjectAltNames(certificate, ALT_DNS_NAME).any {
       verifyHostname(hostname, it)
     }
   }
 
+  /**
+   * This is like [toLowerCase] except that it does nothing if this contains any non-ASCII
+   * characters. We want to avoid lower casing special chars like U+212A (Kelvin symbol) because
+   * they can return ASCII characters that match real hostnames.
+   */
+  private fun String.asciiToLowercase(): String {
+    return when {
+      length == utf8Size().toInt() -> toLowerCase(Locale.US) // This is an ASCII string.
+      else -> this
+    }
+  }
+
   /**
    * Returns true if [hostname] matches the domain name [pattern].
    *
@@ -108,7 +121,7 @@ object OkHostnameVerifier : HostnameVerifier {
     }
     // Hostname and pattern are now absolute domain names.
 
-    pattern = pattern.toLowerCase(Locale.US)
+    pattern = pattern.asciiToLowercase()
     // Hostname and pattern are now in lower case -- domain names are case-insensitive.
 
     if ("*" !in pattern) {

okhttp/src/test/java/okhttp3/HttpUrlTest.java

@@ -1773,6 +1773,17 @@ public void unparseableTopPrivateDomain() {
     assertInvalid("http://../", "Invalid URL host: \"..\"");
   }
 
+  @Test
+  public void hostnameTelephone() throws Exception {
+    // https://www.gosecure.net/blog/2020/10/27/weakness-in-java-tls-host-verification/
+
+    // Map the single character telephone symbol (℡) to the string "tel".
+    assertThat(parse("http://\u2121").host()).isEqualTo("tel");
+
+    // Map the Kelvin symbol (K) to the string "k".
+    assertThat(parse("http://\u212A").host()).isEqualTo("k");
+  }
+
   private void assertInvalid(String string, String exceptionMessage) {
     if (useGet) {
       try {

okhttp/src/test/java/okhttp3/internal/tls/HostnameVerifierTest.java

@@ -24,7 +24,10 @@
 import javax.net.ssl.SSLSession;
 import javax.security.auth.x500.X500Principal;
 import okhttp3.FakeSSLSession;
+import okhttp3.OkHttpClient;
 import okhttp3.internal.Util;
+import okhttp3.tls.HeldCertificate;
+import okhttp3.tls.internal.TlsUtil;
 import org.junit.Ignore;
 import org.junit.Test;
 
@@ -554,6 +557,106 @@ public final class HostnameVerifierTest {
     assertThat(verifier.verify("0:0:0:0:0:FFFF:C0A8:0101", session)).isTrue();
   }
 
+  @Test public void generatedCertificate() throws Exception {
+    HeldCertificate heldCertificate = new HeldCertificate.Builder()
+        .commonName("Foo Corp")
+        .addSubjectAlternativeName("foo.com")
+        .build();
+
+    SSLSession session = session(heldCertificate.certificatePem());
+    assertThat(verifier.verify("foo.com", session)).isTrue();
+    assertThat(verifier.verify("bar.com", session)).isFalse();
+  }
+
+  @Test public void specialKInHostname() throws Exception {
+    // https://github.com/apache/httpcomponents-client/commit/303e435d7949652ea77a6c50df1c548682476b6e
+    // https://www.gosecure.net/blog/2020/10/27/weakness-in-java-tls-host-verification/
+
+    HeldCertificate heldCertificate = new HeldCertificate.Builder()
+        .commonName("Foo Corp")
+        .addSubjectAlternativeName("k.com")
+        .addSubjectAlternativeName("tel.com")
+        .build();
+
+    SSLSession session = session(heldCertificate.certificatePem());
+    assertThat(verifier.verify("foo.com", session)).isFalse();
+    assertThat(verifier.verify("bar.com", session)).isFalse();
+    assertThat(verifier.verify("k.com", session)).isTrue();
+    assertThat(verifier.verify("K.com", session)).isTrue();
+
+    assertThat(verifier.verify("\u2121.com", session)).isFalse();
+    assertThat(verifier.verify("℡.com", session)).isFalse();
+
+    // These should ideally be false, but we know that hostname is usually already checked by us
+    assertThat(verifier.verify("\u212A.com", session)).isFalse();
+    // Kelvin character below
+    assertThat(verifier.verify("K.com", session)).isFalse();
+  }
+
+  @Test public void specialKInCert() throws Exception {
+    // https://github.com/apache/httpcomponents-client/commit/303e435d7949652ea77a6c50df1c548682476b6e
+    // https://www.gosecure.net/blog/2020/10/27/weakness-in-java-tls-host-verification/
+
+    HeldCertificate heldCertificate = new HeldCertificate.Builder()
+        .commonName("Foo Corp")
+        .addSubjectAlternativeName("\u2121.com")
+        .addSubjectAlternativeName("\u212A.com")
+        .build();
+
+    SSLSession session = session(heldCertificate.certificatePem());
+    assertThat(verifier.verify("foo.com", session)).isFalse();
+    assertThat(verifier.verify("bar.com", session)).isFalse();
+    assertThat(verifier.verify("k.com", session)).isFalse();
+    assertThat(verifier.verify("K.com", session)).isFalse();
+
+    assertThat(verifier.verify("tel.com", session)).isFalse();
+    assertThat(verifier.verify("k.com", session)).isFalse();
+  }
+
+  @Test public void specialKInExternalCert() throws Exception {
+    // $ cat ./cert.cnf
+    // [req]
+    // distinguished_name=distinguished_name
+    // req_extensions=req_extensions
+    // x509_extensions=x509_extensions
+    // [distinguished_name]
+    // [req_extensions]
+    // [x509_extensions]
+    // subjectAltName=DNS:℡.com,DNS:K.com
+    //
+    // $ openssl req -x509 -nodes -days 36500 -subj '/CN=foo.com' -config ./cert.cnf \
+    //     -newkey rsa:512 -out cert.pem
+    SSLSession session = session(""
+        + "-----BEGIN CERTIFICATE-----\n"
+        + "MIIBSDCB86ADAgECAhRLR4TGgXBegg0np90FZ1KPeWpDtjANBgkqhkiG9w0BAQsF\n"
+        + "ADASMRAwDgYDVQQDDAdmb28uY29tMCAXDTIwMTAyOTA2NTkwNVoYDzIxMjAxMDA1\n"
+        + "MDY1OTA1WjASMRAwDgYDVQQDDAdmb28uY29tMFwwDQYJKoZIhvcNAQEBBQADSwAw\n"
+        + "SAJBALQcTVW9aW++ClIV9/9iSzijsPvQGEu/FQOjIycSrSIheZyZmR8bluSNBq0C\n"
+        + "9fpalRKZb0S2tlCTi5WoX8d3K30CAwEAAaMfMB0wGwYDVR0RBBQwEoIH4oShLmNv\n"
+        + "bYIH4oSqLmNvbTANBgkqhkiG9w0BAQsFAANBAA1+/eDvSUGv78iEjNW+1w3OPAwt\n"
+        + "Ij1qLQ/YI8OogZPMk7YY46/ydWWp7UpD47zy/vKmm4pOc8Glc8MoDD6UADs=\n"
+        + "-----END CERTIFICATE-----\n");
+
+    assertThat(verifier.verify("tel.com", session)).isFalse();
+    assertThat(verifier.verify("k.com", session)).isFalse();
+
+    assertThat(verifier.verify("foo.com", session)).isFalse();
+    assertThat(verifier.verify("bar.com", session)).isFalse();
+    assertThat(verifier.verify("k.com", session)).isFalse();
+    assertThat(verifier.verify("K.com", session)).isFalse();
+  }
+
+  @Test
+  public void thatCatchesErrorsWithBadSession() {
+    HostnameVerifier localVerifier = new OkHttpClient().hostnameVerifier();
+
+    // Since this is public API, okhttp3.internal.tls.OkHostnameVerifier.verify is also
+    assertThat(verifier).isInstanceOf(OkHostnameVerifier.class);
+
+    SSLSession session = TlsUtil.localhost().sslContext().createSSLEngine().getSession();
+    assertThat(localVerifier.verify("\uD83D\uDCA9.com", session)).isFalse();
+  }
+
   @Test public void verifyAsIpAddress() {
     // IPv4
     assertThat(Util.canParseAsIpAddress("127.0.0.1")).isTrue();