ack 2.00 through 2.11_02 allows remote attackers to execute arbitrary code via a (1) --pager, (2) --regex, or (3) --output option in a .ackrc file in a directory to be searched.
https://github.com/petdance/ack2/issues/399
http://www.securityfocus.com/bid/64196
http://secunia.com/advisories/55982
http://seclists.org/oss-sec/2013/q4/484
http://lists.opensuse.org/opensuse-updates/2014-01/msg00094.html