PgBouncer before 1.5.5 allows remote attackers to cause a denial of service (NULL pointer dereference and crash) by sending a password packet before a startup packet.
https://security.gentoo.org/glsa/201701-24
https://pgbouncer.github.io/changelog.html#pgbouncer-15x
https://github.com/pgbouncer/pgbouncer/commit/edab5be6665b9e8de66c25ba527509b229468573
https://github.com/pgbouncer/pgbouncer/commit/74d6e5f7de5ec736f71204b7b422af7380c19ac5