The version of the bundled Atlassian OAuth plugin was vulnerable to Server Side Request Forgery (SSRF). This allowed a XSS and or a SSRF attack to be performed. More information about the Atlassian OAuth plugin issue see https://ecosystem.atlassian.net/browse/OAUTH-344 . When running in an environment like Amazon EC2, this flaw can used to access to a metadata resource that provides access credentials and other potentially confidential information.

Workaround for Confluence - In case you can't upgrade yet to 6.1.3:

1. Shutdown Confluence.
2. Go to <Confluence-Installation-Directory>/confluence/WEB-INF/atlassian-bundled-plugins and find the atlassian-oauth-service-provider-plugin-2.0.2.jar file.
3. Delete it.
4. Download below file, which is the atlassian-oauth-service-provider-plugin-2.0.4.jar file for Confluence:
   atlassian-oauth-service-provider-plugin-2.0.4.jar
5. Paste it inside <Confluence-Installation-Directory>/confluence/WEB-INF/atlassian-bundled-plugins folder.
6. Clear plugin cache.
7. Bring Confluence back online.