dovecot -- abort of SASL authentication results in a memory leak

Pedro Sampaio reports:

A flaw was found in dovecot 2.0 up to 2.2.33 and 2.3.0. A abort of
SASL authentication results in a memory leak in Dovecot auth client
used by login processes. The leak has impact in high performance
configuration where same login processes are reused and can cause the
process to crash due to memory exhaustion.