Original version http://www.security.nnov.ru/advisories/courier.asp Title: Courier CPU exhaustion Author: ZARAZA <3APA3Aat_private> Date: May, 31 2002 Affected: courier-0.38.1 Vendor: Double Precision, Inc. Risk: Low to average Remote: Yes Exploitable: Yes Vendor notified: May, 20 2002 Product URL: http://www.courier-mta.org SECURITY.NNOV URL: http://www.security.nnov.ru Advanced info: http://www.security.nnov.ru/search/news.asp?binid=2055 Introduction: Courier is widely used suite of e-mail services written with security in mind. Problem: A loop with unchecked iteration counter controlled by user input may cause courier to freeze for over the minute with 100% CPU usage on single command or message. Details: rfc822_parsedt.c: unsigned day=0, mon=0, year; ... unsigned y; ... if (year < 1970) return (0); ... for (y=1970; y<year; y++) ... year may be any unsigned integer. Vendor: Sam Varshavchik <mrsam@courier-mta.com> was contacted on May, 20. Problem was patched in CVS version on the same day. -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Bonus on imap-uw: Imap-uw allows user to access any file he could access locally. It's not a bug it's insecurity by design (it was not created with security in mind ;-). According FAQ from vendor's web site (it's not mentioned in a FAQ inside program distribution): -=-=-=-=-=-=- 5.1 I see that the IMAP server allows access to arbitary files on the system, including /etc/passwd! How do I disable this? You should not worry about this if your IMAP users are allowed shell access. The IMAP server does not permit any access that the user can not have via the shell. If, and only if, you deny your IMAP users shell access, you may want to consider one of three choices. Note that these choices reduce IMAP functionality, and may have undesirable side effects. Each of these choices involves an edit to file src/osdep/unix/env_unix.c The first (and recommended) choice is to set restrictBox as described in file CONFIG. This will disable access to the filesystem root, to other users' home directory, and to superior directory. The second (and strongly NOT recommended) choice is to set closedBox as described in file CONFIG. This puts each IMAP session into a so-called "chroot jail", and thus setting this option is extremely dangerous; it can make your system much less secure and open to root compromise attacks. So do not use this option unless you are absolutely certain that you understand all the issues of a "chroot jail." The third choice is to rewrite routine mailboxfile() to implement whatever mapping from mailbox name to filesystem name (and restrictions) that you wish. This is the most general choice. As a guide, you can see at the start of routine mailboxfile() what the restrictBox choice does. -=-=-=-=-=- It should be noted that restrictBox/closedBox is not described in neither CONFIG nor any other document from program distribution at all (as for imap-2001a)... And even if you smart enough to check the FAQ on the web site after you red the FAQ in source distribution restrictBox can be bypassed in case of any Windows builds (for example http://sourceforge.net/projects/uw-imap-cygwin/) because '\\' symbol is never checked. Hope nobody uses UW under NT or a version from OS ports distribution in production environment because as far as I can see port maintainers do not change the value of closedBox :). I'm not sure if there are utilities to access file system via imap-uw, a created a small set of tools you can download imaptools.tgz from http://www.security.nnov.ru/search/news.asp?binid=2063 it includes: imapget.c - to retrieve file via imap-uw, usage example: imapget imap.host.name /etc/passwd > passwd it should work for both text and binary files. imapls.c - to get a file listing, usage example: imapls imaphostname /tmp/\* > ls-tmp imaprm.c, imapmkdir.c - hope you catch the idea. it's also possible to create file with any name in mailbox format. -- http://www.security.nnov.ru /\_/\ { , . } |\ +--oQQo->{ ^ }<-----+ \ | ZARAZA U 3APA3A } +-------------o66o--+ / |/ You know my name - look up my number (The Beatles)
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