The nginx package before 1.6.2-5+deb8u3 on Debian jessie, the nginx packages before 1.4.6-1ubuntu3.6 on Ubuntu 14.04 LTS, before 1.10.0-0ubuntu0.16.04.3 on Ubuntu 16.04 LTS, and before 1.10.1-0ubuntu1.1 on Ubuntu 16.10, and the nginx ebuild before 1.10.2-r3 on Gentoo allow local users with access to the web server user account to gain root privileges via a symlink attack on the error log.
https://security.gentoo.org/glsa/201701-22
http://www.ubuntu.com/usn/USN-3114-1
http://www.securitytracker.com/id/1037104
http://www.securityfocus.com/bid/93903
http://www.securityfocus.com/archive/1/539796/100/0/threaded
http://www.debian.org/security/2016/dsa-3701