Ansible before 1.6.7 does not prevent inventory data with "{{" and "lookup" substrings, and does not prevent remote data with "{{" substrings, which allows remote attackers to execute arbitrary code via (1) crafted lookup('pipe') calls or (2) crafted Jinja2 data.
https://github.com/ansible/ansible/commit/62a1295a3e08cb6c3e9f1b2a1e6e5dcaeab32527