The add_job function in scheduler/ipp.c in CUPS before 2.2.6, when D-Bus support is enabled, can be crashed by remote attackers by sending print jobs with an invalid username, related to a D-Bus notification.
https://github.com/apple/cups/releases/tag/v2.2.6
https://github.com/apple/cups/commit/49fa4983f25b64ec29d548ffa3b9782426007df3