In 2013 the security chapter of the Handbook was updated in r42501 to suggest limiting access to the system accounting file [*1] by creating the initial file with a mode of 0600. This was in part based on a discussion in the forums [*2]. Unfortunately, this advice is overridden by the fact that a new file is created as part of periodic daily processing, and the file mode is set by the rc.d/accounting script.
These changes update the accounting script to create the directory with mode 0750 if it doesn't already exist, and to create the daily file with mode 0640. This limits write access to root only, read access to root and members of wheel, and eliminates world access completely. For admins who want to prevent even members of wheel from accessing the files, the mode of the /var/account directory can be manually changed to 0700, because the script never creates or changes that directory if it already exists.
The accounting_rotate_log() function now also handles the error cases of no existing log file to rotate, and attempting to rotate the file multiple times (.0 file already exists).
Another small change here eliminates the complexity of the mktemp/chmod/mv sequence for creating a new acct file by just using touch with the appropriate umask to directly create the file with the desired modes. That allows coalescing two separate if checkyesno accounting_enable blocks into one.
These changes were inspired by my investigation of PR 202203.
[1] https://www.freebsd.org/doc/handbook/security-accounting.html
[2] http://forums.freebsd.org/showthread.php?t=41059