click/install.py in click does not require files in package filesystem tarballs to start with ./ (dot slash), which allows remote attackers to install an alternate security policy and gain privileges via a crafted package, as demonstrated by the test.mmrow app for Ubuntu phone.
bazaar.launchpad.net/~click-hackers/click/devel/revision/587
ubuntu.com/usn/usn-2771-1
www.openwall.com/lists/oss-security/2016/01/12/8
www.securityfocus.com/bid/96386
bugs.launchpad.net/ubuntu/+source/click/+bug/1506467
code.launchpad.net/~cjwatson/click/audit-missing-dot-slash/+merge/274554
insights.ubuntu.com/2015/10/15/update-on-ubuntu-phone-security-issue/
plus.google.com/+SzymonWaliczek/posts/3jbG2uiAniF