Tor 0.3.x before 0.3.0.9 has a guard-selection algorithm that only considers the exit relay (not the exit relay's family), which might allow remote attackers to defeat intended anonymity properties by leveraging the existence of large families.
https://trac.torproject.org/projects/tor/ticket/22753
https://security-tracker.debian.org/CVE-2017-0377
https://github.com/torproject/tor/commit/665baf5ed5c6186d973c46cdea165c0548027350
https://blog.torproject.org/blog/tor-0314-alpha-released-security-update-clients
https://blog.torproject.org/blog/tor-0309-released-security-update-clients