Apache Tika provides optional functionality to run itself as a web service to allow remote use. When used in this 
manner, it's possible for a 3rd party to pass a 'fileUrl' header to the Apache Tika Server (tika-server).
This header lets a remote client request that the server fetches content from the URL provided, including files
from the server's local filesystem.
Depending on the file permissions set on the local filesystem, this could be used to return sensitive content from 
the server machine.

This vulnerability only exists if you are running the tika-server version 1.9, and you allow un-trusted access
to the tika-server URL. Usage of Apache Tika as a standard library is not affected.

Mitigation:
Apache Tika 1.9 users should upgrade to Apache Tika 1.10

Reference:

http://seclists.org/oss-sec/2015/q3/350