Fix References header parser for Microsoft Exchange

Microsoft Exchange would append a comma and another
message id into the References header, therefore we'll
need to fallback and parse the header by ourselves.

Closes #26567

2 files changed, 20 insertions, 6 deletions

diff --git a/lib/gitlab/email/receiver.rb b/lib/gitlab/email/receiver.rb
index a40c44eb1bc..df9d1cae8da 100644
--- a/lib/gitlab/email/receiver.rb
+++ b/lib/gitlab/email/receiver.rb
@@ -35,6 +35,8 @@ module Gitlab
         handler.execute
       end
 
+      private
+
       def build_mail
         Mail::Message.new(@raw)
       rescue Encoding::UndefinedConversionError,
@@ -54,7 +56,20 @@ module Gitlab
       end
 
       def key_from_additional_headers(mail)
-        Array(mail.references).find do |mail_id|
+        find_key_from_references(ensure_references_array(mail.references))
+      end
+
+      def ensure_references_array(references)
+        case references
+        when Array
+          references
+        when String # Handle emails from Microsoft exchange which uses commas
+          Gitlab::IncomingEmail.scan_fallback_references(references)
+        end
+      end
+
+      def find_key_from_references(references)
+        references.find do |mail_id|
           key = Gitlab::IncomingEmail.key_from_fallback_message_id(mail_id)
           break key if key
         end
diff --git a/lib/gitlab/incoming_email.rb b/lib/gitlab/incoming_email.rb
index 801dfde9a36..9ae3a2c1214 100644
--- a/lib/gitlab/incoming_email.rb
+++ b/lib/gitlab/incoming_email.rb
@@ -3,8 +3,6 @@ module Gitlab
     WILDCARD_PLACEHOLDER = '%{key}'.freeze
 
     class << self
-      FALLBACK_MESSAGE_ID_REGEX = /\Areply\-(.+)@#{Gitlab.config.gitlab.host}\Z/.freeze
-
       def enabled?
         config.enabled && config.address
       end
@@ -32,10 +30,11 @@ module Gitlab
       end
 
       def key_from_fallback_message_id(mail_id)
-        match = mail_id.match(FALLBACK_MESSAGE_ID_REGEX)
-        return unless match
+        mail_id[/\Areply\-(.+)@#{Gitlab.config.gitlab.host}\z/, 1]
+      end
 
-        match[1]
+      def scan_fallback_references(references)
+        references.scan(/(?!<)[^<>]+(?=>)/.freeze)
       end
 
       def config