The OAuthHelper in Atlassian Application Links before version 5.0.10, from version 5.1.0 before version 5.1.3, and from version 5.2.0 before version 5.2.6 used an XML document builder that was vulnerable to XXE when consuming a client OAuth request. This allowed malicious oauth application linked applications to probe internal network resources by requesting internal locations, read the contents of files and also cause an out of memory exception affecting availability via an XML External Entity vulnerability.