CVE-2019-19783

An issue was discovered in Cyrus IMAP before 2.5.15, 3.0.x before 3.0.13, and 3.1.x through 3.1.8. If sieve script uploading is allowed (3.x) or certain non-default sieve options are enabled (2.x), a user with a mail account on the service can use a sieve script containing a fileinto directive to create any mailbox with administrator privileges, because of folder mishandling in autosieve_createfolder() in imap/lmtp_sieve.c.

Mitigation

This flaw can be mitigated by:
1. In cyrus-imapd >= 2.5 disable anysievefolder (it is disabled by default)
2. In cyrus-imapd >=3.0 disable sieve_extensions