Marco Nenciarini uploaded new packages for dovecot which fixed the
following security problems:

CVE-2010-3706
  plugins/acl/acl-backend-vfile.c in Dovecot 1.2.x before 1.2.15 and
  2.0.x before 2.0.5 interprets an ACL entry as a directive to add to
  the permissions granted by another ACL entry, instead of a directive
  to replace the permissions granted by another ACL entry, in certain
  circumstances involving the private namespace of a user, which allows
  remote authenticated users to bypass intended access restrictions via
  a request to read or modify a mailbox.

  http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2010-3706

CVE-2010-3707
  plugins/acl/acl-backend-vfile.c in Dovecot 1.2.x before 1.2.15 and
  2.0.x before 2.0.5 interprets an ACL entry as a directive to add to
  the permissions granted by another ACL entry, instead of a directive
  to replace the permissions granted by another ACL entry, in certain
  circumstances involving more specific entries that occur after less
  specific entries, which allows remote authenticated users to bypass
  intended access restrictions via a request to read or modify a
  mailbox.

  http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2010-3707

CVE-2010-3779
  Dovecot 1.2.x before 1.2.15 and 2.0.x before 2.0.beta2 grants the
  admin permission to the owner of each mailbox in a non-public
  namespace, which might allow remote authenticated users to bypass
  intended access restrictions by changing the ACL of a mailbox, as
  demonstrated by a symlinked shared mailbox.

  http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2010-3779

CVE-2010-3780
  Dovecot 1.2.x before 1.2.15 allows remote authenticated users to
  cause a denial of service (master process outage) by simultaneously
  disconnecting many (1) IMAP or (2) POP3 sessions.

  http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2010-3780

For the lenny-backports distribution the problems have been fixed in
version 1.2.15-1~bpo50+1.

For the current testing (squeeze) and unstable (sid) distributions, the
problem has been fixed in version 1.2.15-1.

Upgrade instructions
--------------------

If you don't use pinning (see [1]) you have to update the package
manually via "apt-get -t lenny-backports install <packagelist>" with
the packagelist of your installed packages affected by this update.
[1] <https://backports.debian.org/Instructions>

We recommend to pin the backports repository to 200 so that new
versions of installed  backports will be installed automatically.

  Package: *
  Pin: release a=lenny-backports
  Pin-Priority: 200