#171: fixed bug where "References" header raised a CRLF Injection fla…

…g. Also added test to verify the "References" header is filled properly by replying multiple times in a thread.

src/main/java/org/simplejavamail/mailer/Mailer.java

@@ -21,6 +21,7 @@
 import javax.mail.PasswordAuthentication;
 import javax.mail.Session;
 import javax.mail.internet.MimeMessage;
+import javax.mail.internet.MimeUtility;
 import java.util.EnumSet;
 import java.util.Map;
 import java.util.Properties;
@@ -302,7 +303,11 @@ public boolean validate(final Email email)
 		scanForInjectionAttack(email.getSubject(), "email.subject");
 		for (final Map.Entry<String, String> headerEntry : email.getHeaders().entrySet()) {
 			scanForInjectionAttack(headerEntry.getKey(), "email.header.mapEntryKey");
-			scanForInjectionAttack(headerEntry.getValue(), "email.header." + headerEntry.getKey());
+			if (headerEntry.getKey().equals("References")) {
+				scanForInjectionAttack(MimeUtility.unfold(headerEntry.getValue()), "email.header.References");
+			} else {
+				scanForInjectionAttack(headerEntry.getValue(), "email.header." + headerEntry.getKey());
+			}
 		}
 		for (final AttachmentResource attachment : email.getAttachments()) {
 			scanForInjectionAttack(attachment.getName(), "email.attachment.name");
@@ -331,6 +336,11 @@ public boolean validate(final Email email)
 	/**
 	 * @param value      Value checked for suspicious newline characters "\n", "\r" and "%0A" (as acknowledged by SMTP servers).
 	 * @param valueLabel The name of the field being checked, used for reporting exceptions.
+	 *
+	 * @see <a href="http://www.cakesolutions.net/teamblogs/2008/05/08/email-header-injection-security">http://www.cakesolutions.net/teamblogs/2008/05/08/email-header-injection-security</a>
+	 * @see <a href="https://security.stackexchange.com/a/54100/110048">https://security.stackexchange.com/a/54100/110048</a>
+	 * @see <a href="https://www.owasp.org/index.php/Testing_for_IMAP/SMTP_Injection_(OTG-INPVAL-011)">https://www.owasp.org/index.php/Testing_for_IMAP/SMTP_Injection_(OTG-INPVAL-011)</a>
+	 * @see <a href="http://cwe.mitre.org/data/definitions/93.html">http://cwe.mitre.org/data/definitions/93.html</a>
 	 */
 	private static void scanForInjectionAttack(final String value, final String valueLabel) {
 		if (value != null && (value.contains("\n") || value.contains("\r") || value.contains("%0A"))) {

src/test/java/org/simplejavamail/mailer/MailerLiveTest.java

@@ -17,9 +17,11 @@
 
 import javax.mail.MessagingException;
 import javax.mail.internet.MimeMessage;
+import javax.mail.internet.MimeUtility;
 import java.io.IOException;
 import java.util.Properties;
 
+import static java.lang.String.format;
 import static javax.mail.Message.RecipientType.TO;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.data.MapEntry.entry;
@@ -138,7 +140,7 @@ private Email assertSendingEmail(final EmailPopulatingBuilder originalEmailPopul
 
 	@Test
 	public void createMailSession_ReplyToMessage()
-			throws IOException, MessagingException {
+			throws MessagingException {
 		// send initial mail
 		mailer.sendMail(readOutlookMessage("test-messages/HTML mail with replyto and attachment and embedded image.msg").buildEmail());
 		MimeMessage receivedMimeMessage = smtpServerRule.getOnlyMessage();
@@ -170,7 +172,7 @@ public void createMailSession_ReplyToMessage()
 
 	@Test
 	public void createMailSession_ReplyToMessage_NotAll_AndCustomReferences()
-			throws IOException, MessagingException {
+			throws MessagingException {
 		// send initial mail
 		mailer.sendMail(readOutlookMessage("test-messages/HTML mail with replyto and attachment and embedded image.msg").buildEmail());
 		MimeMessage receivedMimeMessage = smtpServerRule.getOnlyMessage();
@@ -179,20 +181,42 @@ public void createMailSession_ReplyToMessage_NotAll_AndCustomReferences()
 		// send reply to initial mail
 		Email reply = EmailBuilder
 				.replyingTo(assertSendingEmail(receivedEmailPopulatingBuilder, false))
-				.withHeader("References", "dummy-references")
-				.from("dummy@domain.com")
+				.from("Moo Shmoo", "dummy@domain.com")
 				.withPlainText("This is the reply")
 				.buildEmail();
 
 		// test received reply to initial mail
 		mailer.sendMail(reply);
-		MimeMessage receivedMimeMessageReply1 = smtpServerRule.getOnlyMessage("lo.pop.replyto@somemail.com");
-		Email receivedReply = mimeMessageToEmail(receivedMimeMessageReply1);
+		MimeMessage receivedMimeMessageReply = smtpServerRule.getOnlyMessage("lo.pop.replyto@somemail.com");
+		Email receivedReply = mimeMessageToEmail(receivedMimeMessageReply);
 
 		EmailAssert.assertThat(receivedReply).hasSubject("Re: hey");
 		EmailAssert.assertThat(receivedReply).hasOnlyRecipients(new Recipient("lollypop-replyto", "lo.pop.replyto@somemail.com", TO));
 		assertThat(receivedReply.getHeaders()).contains(entry("In-Reply-To", receivedEmailPopulatingBuilder.getId()));
-		assertThat(receivedReply.getHeaders()).contains(entry("References", "dummy-references"));
+		assertThat(receivedReply.getHeaders()).contains(entry("References", receivedEmailPopulatingBuilder.getId()));
+
+		EmailPopulatingBuilder receivedEmailReplyPopulatingBuilder = mimeMessageToEmailBuilder(receivedMimeMessageReply);
+
+		Email replyToReply = EmailBuilder
+				.replyingTo(assertSendingEmail(receivedEmailReplyPopulatingBuilder, false))
+				.from("Pappa Moo", "dummy@domain.com")
+				.withPlainText("This is the reply to the reply")
+				.buildEmail();
+
+		// test received reply to initial mail
+		mailer.sendMail(replyToReply);
+		MimeMessage receivedMimeMessageReplyToReply = smtpServerRule.getOnlyMessage("dummy@domain.com");
+		Email receivedReplyToReply = mimeMessageToEmail(receivedMimeMessageReplyToReply);
+
+		EmailAssert.assertThat(receivedReplyToReply).hasSubject("Re: hey");
+		EmailAssert.assertThat(receivedReplyToReply).hasOnlyRecipients(new Recipient("Moo Shmoo", "dummy@domain.com", TO));
+		assertThat(receivedReplyToReply.getHeaders()).contains(entry("In-Reply-To", receivedEmailReplyPopulatingBuilder.getId()));
+
+		assertThat(receivedReplyToReply.getHeaders()).contains(entry("References",
+				MimeUtility.fold("References: ".length(), format("%s\n%s",
+						receivedEmailPopulatingBuilder.getId(),
+						receivedEmailReplyPopulatingBuilder.getId()))
+		));
 	}
 
 	private void assertAttachmentMetadata(AttachmentResource embeddedImg, String mimeType, String filename) {