Revive Adserver before 3.2.3 suffers from session fixation, by allowing arbitrary session identifiers to be forced and, at the same time, by not invalidating the existing session upon a successful authentication. Under some circumstances, that could have been an opportunity for an attacker to steal an authenticated session.
https://www.revive-adserver.com/security/revive-sa-2016-001/
https://hackerone.com/reports/93813
https://hackerone.com/reports/93809
https://github.com/revive-adserver/revive-adserver/commit/4910365631eabbb208961c36149f41cc8159fb39