the folks of the "Serendipity (S9Y) blog CMS" community, namely Garvin
Hicking, has enhanced S9Y to log attempts to log into the CMS's backend.
The logs meet the requirements for fail2ban.
I enclose a plain text file describing the details on how to configure
fail2ban for the logfile of Serendipity.
Whoever feels responsible might include the configuration example and
information into fail2bans repository and the packages / ports for the
various Linux / Unix distributions.
I personally believe, it was an enrichment to also provide some examples for
logfiles from web CMS as often their backends are quite unprotected.