URLTrigger Plugin 0.48 and earlier does not configure its XML parser to prevent XML external entity (XXE) attacks.
This allows attackers with Job/Configure permission or otherwise able to control the contents of an URL to an XML document being examined for changes to have Jenkins parse a crafted XML document that uses external entities for extraction of secrets from the polling Jenkins controller or agent, server-side request forgery, or denial-of-service attacks.
URLTrigger Plugin 0.49 disables external entity resolution for its XML parser.