sendmail is a widely-used Mail Transport Agent (MTA).
The sm_close_on_exec function in conf.c has arguments in the wrong order.
A local attacker could get access to unintended high-numbered file descriptors via a specially crafted program.
There is no known workaround at this time.
All sendmail users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=mail-mta/sendmail-8.14.9"