Jinja2, a template engine written in pure python, was found to use /tmp as a default directory for jinja2.bccache.FileSystemBytecodeCache, which is insecure because the /tmp directory is world-writable and the filenames used by FileSystemBytecodeCache are predictable. A malicious local user could exploit this bug to alter output generated by other user's application using Jinja2 or possibly, execute arbitrary code as another user.

References: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=734747