Cybozu Mailwise 5.0.4 and 5.0.5 allows remote authenticated users to obtain sensitive e-mail content intended for different persons in opportunistic circumstances by reading Subject header lines within the user's own mailbox.
http://jvndb.jvn.jp/jvndb/JVNDB-2013-000077
http://jvn.jp/en/jp/JVN21103639/index.html