Squid security advisory 2015:1 reports:
Squid configured with client-first SSL-bump does not correctly validate X509 server certificate domain / hostname fields. The bug is important because it allows remote servers to bypass client certificate validation. Some attackers may also be able to use valid certificates for one domain signed by a global Certificate Authority to abuse an unrelated domain. However, the bug is exploitable only if you have configured Squid to perform SSL Bumping with the "client-first" or "bump" mode of operation. Sites that do not use SSL-Bump are not vulnerable. All Squid built without SSL support are not vulnerable to the problem.
The FreeBSD port does not use SSL by default and is not vulnerable in the default configuration.