Cyrus IMAP 3.8.3 Release Notes

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Changes since 3.8.2

Security fixes

  • Fixed 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 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.