An issue was discovered in ownCloud before 10.4. Because of an SSRF issue (via the apps/files_sharing/external remote parameter), an authenticated attacker can interact with local services blindly (aka Blind SSRF) or conduct a Denial Of Service attack.
https://owncloud.org/changelog/server/
https://owncloud.com/security-advisories/ssrf-in-add-to-your-owncloud-functionality/
https://blog.hacktivesecurity.com/index.php?controller=post&action=view&id_post=44