The bundled Atlassian Universal Plugin Manager plugin had a XXE issue - CVE-2018-20233

The version of the bundled Atlassian Universal Plugin Manager plugin had a XML External Entity vulnerability that allowed remote attackers with system administrator privileges to read files, make network requests and perform a denial of service attack via an XML External Entity vulnerability in the parsing of atlassian plugin xml files in an uploaded JAR. See https://ecosystem.atlassian.net/browse/UPM-5964 for more details.