When preparing the query for finding events for the Manage Events page, the event type parameter was not properly escaped.
CiviCRM versions 5.13.0 and earlier
CiviCRM version 5.13.4 and 5.7.6
Upgrade to latest CiviCRM
Allen Shaw of Joinery for reporting the issue
Seamus Lee of Australian Greens for fixing the issue
security/core#51