Microsoft SharePoint Portal Server 2003 SP3 and SharePoint Server 2007 SP3, 2010 SP1 and SP2, and 2013 do not properly process unassigned workflows, which allows remote attackers to cause a denial of service (W3WP process hang) via a crafted URL, aka "SharePoint Denial of Service Vulnerability."
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A19036
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2013/ms13-067