March 2008 - Dovecot-news

v1.0.13 and v1.1.rc3 released
by Timo Sirainen 09 Mar '08

09 Mar '08

http://dovecot.org/releases/1.0/dovecot-1.0.13.tar.gz http://dovecot.org/releases/1.0/dovecot-1.0.13.tar.gz.sig http://dovecot.org/releases/1.1/rc/dovecot-1.1.rc3.tar.gz http://dovecot.org/releases/1.1/rc/dovecot-1.1.rc3.tar.gz.sig Note that the changes for the security hole fix were quite large. I tested with several auth configurations myself and they seemed to work, but it's possible I left a bug somewhere in there breaking someone's configuration. So make sure to test that it works after upgrading. Of course it would be really nice if Dovecot had a proper test suite where testing all configurations could be automated and run before each release. I've already started this with my imaptest tool (http://imapwiki.org/ImapTest), but it only does IMAP tests and a lot of things are still missing. Some help would be nice here. * Fixed a security hole in blocking passdbs (MySQL always. PAM, passwd and shadow if blocking=yes) where user could specify extra fields in the password. The main problem here is when specifying "skip_password_check" introduced in v1.0.11 for fixing master user logins, allowing the user to log in as anyone without a valid password. - mail_privileged_group was broken in some systems (OS X, Solaris?) - IMAP THREAD: Fixed some correctness problems

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Security hole #6: Some passdbs allowed users to log in without a valid password
by Timo Sirainen 09 Mar '08

09 Mar '08

This affects only blocking passdbs: - MySQL - PAM, passwd and shadow if blocking=yes The underlying bug exists in all v1.0.x versions, but I couldn't figure out a way to exploit it except with v1.0.11, v1.0.12 and v1.1.rc2. Probably a good idea to upgrade in any case. The main problem is that Dovecot's internal protocols use TAB character as a delimiter, but passwords were sent unescaped through them. So passwords containing TAB characters allowed to add new internal fields. The main problem here is a new "skip_password_check" field added in v1.0.11 to fix problems with master user logins. Specifying this field allowed the user to skip the password check, as the name implies. This has been fixed thoroughly in v1.0.13 and v1.1.rc3 to make sure there are no more escaping problems with any fields, but it can be also fixed with a less intrusive patch for v1.0: http://hg.dovecot.org/dovecot-1.0/raw-rev/da2a9372e26e

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v1.1.rc2 released
by Timo Sirainen 08 Mar '08

08 Mar '08

http://dovecot.org/releases/1.1/rc/dovecot-1.1.rc2.tar.gz http://dovecot.org/releases/1.1/rc/dovecot-1.1.rc2.tar.gz.sig Changes since rc1: * mail_extra_groups setting was commonly used insecurely. This setting is now deprecated. Most users should switch to using mail_privileged_group setting, but if you really need the old functionality use mail_access_groups instead. + Expire plugin now supports wildcards in mailbox names. + dbox: Expire plugin supports moving old mails to alternative dbox directory + Maildir++ quota: quota_rule=?:<rule> specifies a default rule which is used only if the maildirsize file doesn't exist. + If SSL/TLS connection isn't closed cleanly, log the last error in the disconnection line. + EXPUNGE: If new \Deleted messages were found while expunging, do it again and expunge them as well (Outlook workaround) - IMAP: SEARCH, LIST and THREAD command correctness fixes - Maildir++ quota: Quota rules and warnings with % rules didn't work if the default limits were taken from maildirsize file. - Maildir++ quota: If both byte and message limits weren't specified, maildirsize file was recalculated all the time - mbox: Flag and keyword updates may have gotten lost in some situations (happens with v1.0 too) - ldap: Don't crash if userdb lookup fails - Squat fixes and performance improvements Things left to do for v1.1.0: - dbox has a metadata corruption bug, find and fix it - Squat has some locking issues that causes errors when stress testing with multiple connections - Squat doesn't do NFS cache flushing and has some other NFS problems.

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v1.0.12 released
by Timo Sirainen 05 Mar '08

05 Mar '08

http://dovecot.org/releases/1.0/dovecot-1.0.12.tar.gz http://dovecot.org/releases/1.0/dovecot-1.0.12.tar.gz.sig - Using mail_privileged_group with dotlock_use_excl=no worked, but it logged "access denied" errors.

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v1.0.11 released
by Timo Sirainen 04 Mar '08

04 Mar '08

http://dovecot.org/releases/1.0/dovecot-1.0.11.tar.gz http://dovecot.org/releases/1.0/dovecot-1.0.11.tar.gz.sig * mail_extra_groups setting was commonly used insecurely. This setting is now deprecated. Most users should switch to using mail_privileged_group setting, but if you really need the old functionality use mail_access_groups instead. - mbox: Dropped some of the physical size fetch optimizations added in v1.0.8. This makes some commands slower, but should fix the rest of the problems. - IMAP: SEARCH BEFORE/ON/SINCE didn't handle timezones correctly. - ldap: auth_bind was doing lookups using subtree scope instead of the scope specified in config file. - zlib plugin crashfixes by Richard Platel - master passdbs: pass=yes setting was broken with blocking passdbs (e.g. MySQL)

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Security issue #5: mail_extra_groups setting is often used insecurely
by Timo Sirainen 04 Mar '08

04 Mar '08

mail_extra_groups=mail setting is often used insecurely to give Dovecot access to create dotlocks to /var/mail directory. If you don't use mboxes in /var/mail, make sure this setting is cleared. If you do use /var/mail mboxes and Dovecot gives permission errors without it, do one of the following (in the preferred order): a) Upgrade to v1.0.11 and use the new mail_privileged_group setting instead of mail_extra_groups. b) Make /var/mail sticky and world-writable (chmod 01777 /var/mail) and clear mail_extra_groups setting. c) Make /var/mail sticky (chmod +t /var/mail) and keep mail_extra_groups setting. This fixes the main problem but some may be left. The mail_privileged_group setting is also available as a patch: http://dovecot.org/patches/1.0/dovecot-1.0.10.mail_priv_groups.diff mail_extra_groups setting has existed since Dovecot v0.99.10.6. It's never been enabled by default in the distributed dovecot-example.conf, but some distributions enable it by default (at least Debian). A longer explanation: The main problem is that if users have filesystem access to the mail server, they can create symlinks. Dovecot doesn't try to prevent following symlinks (and I don't think it should) and normally it isn't a problem. But when mail_extra_groups=mail is set: 1a) Maildir: Any files readable by mail group can be read by the user by symlinking the file to their ~/Maildir/cur/. 1b) Any mbox files readable by mail group can be read by the user by symlinking the mbox file to their ~/mail/ directory. These are pretty obvious problems and I didn't think they were all that important. Why would anyone have secret files that are mail group-readable? But apparently those do exist in some systems (maybe accidentally). 2a) mbox: Any files/directories under mail group-writable directories can be created/deleted/renamed by symlinking the directory under ~/mail/. For example ln -s /var/mail ~/mail/var, DELETE var/root will happily delete root's mailbox. This I hadn't thought about before. 2b) Maildir: Pretty much the same thing can be done with maildir but with a little less control. mail_privileged_group setting works by keeping the group in process's saved GID while it's not in use and temporarily switching it to effective GID while dotlocks are created. Currently this is done only when: 1. It's only done for INBOX mbox which doesn't exist under the same location as other mailboxes (so typically under /var/mail). 2. It's used only after initial dotlock creation try failed with EACCES error.

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