mod_session_dbd.c in the mod_session_dbd module in the Apache HTTP Server before 2.4.5 proceeds with save operations for a session without considering the dirty flag and the requirement for a new session ID, which has unspecified impact and remote attack vectors.
https://httpd.apache.org/security/vulnerabilities_24.html
http://kb.juniper.net/InfoCenter/index?page=content&id=JSA10698