[原文]The 55_options_traceback.dpatch patch for mailman 2.1.5 in Ubuntu 4.10 displays a different error message depending on whether the e-mail address is subscribed to a private list, which allows remote attackers to determine the list membership for a given e-mail address.
Mailman contains a flaw that may lead to an unauthorized information disclosure. The issue is triggered when a malicious user sends a special request, resulting in an error message which will disclose subscription status information regarding a particular email address resulting in a loss of confidentiality.
Upgrade to version 2.1.5-1ubuntu2.2 or higher, as it has been reported to fix this vulnerability. An upgrade is required as there are no known workarounds.