Exim through 4.97.1 misparses a multiline RFC 2231 header filename, and thus remote attackers can bypass a $mime_filename extension-blocking protection mechanism, and potentially deliver executable attachments to the mailboxes of end users.
https://www.rfc-editor.org/rfc/rfc2231.txt
https://github.com/Exim/exim/compare/exim-4.98-RC2...exim-4.98-RC3
https://git.exim.org/exim.git/commit/6ce5c70cff8989418e05d01fd2a57703007a6357
https://git.exim.org/exim.git/commit/1b3209b0577a9327ebb076f3b32b8a159c253f7b