The nginx package before 1.6.2-5+deb8u3 on Debian jessie and 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 allow local users with access to the web server user account to gain root privileges via a symlink attack on the error log.