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Cyrus IMAP 3.8.3 Release Notes
==============================

Download from GitHub:

* https://github.com/cyrusimap/cyrus-imapd/releases/download/cyrus-imapd-3.8.3/cyrus-imapd-3.8.3.tar.gz
* https://github.com/cyrusimap/cyrus-imapd/releases/download/cyrus-imapd-3.8.3/cyrus-imapd-3.8.3.tar.gz.sig

.. _relnotes-3.8.3-changes:

Changes since 3.8.2
===================

Security fixes
--------------

* Fixed :cve:`CVE-2024-34055`:
  Cyrus-IMAP through 3.8.2 and 3.10.0-beta2 allow authenticated attackers
  to cause unbounded memory allocation by sending many LITERALs in a
  single command.

  The IMAP protocol allows for command arguments to be LITERALs of
  negotiated length, and for these the server allocates memory to
  receive the content before instructing the client to proceed. The
  allocated memory is released when the whole command has been received
  and processed.

  The IMAP protocol has a number commands that specify an unlimited
  number of arguments, for example SEARCH. Each of these arguments can
  be a LITERAL, for which memory will be allocated and not released
  until the entire command has been received and processed. This can run
  a server out of memory, with varying consequences depending on the
  server's OOM policy.

  Discovered by Damian Poddebniak.

  Two limits, with corresponding :cyrusman:`imapd.conf(5)` options, have
  been added to address this:

  * ``maxargssize`` (default: unlimited): limits the overall length of a
    single IMAP command.  Deployments should configure this to a size that
    suits their system resources and client usage patterns
  * ``maxliteral`` (default: 128K): limits the length of individual IMAP
    LITERALs

  Connections sending commands that would exceed these limits will see the
  command fail, or the connection closed, depending on the specific context.
  The error message will contain the ``[TOOBIG]`` response code.

  These limits may be set small without affecting message uploads, as the
  APPEND command's message literal is limited by ``maxmessagesize``, not by
  these new options.
