/usr/lib/python2.7/dist-packages/sagenb/data/jquery/plugins/form is in python-sagenb 1.0.1+ds1-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/python2.7/dist-packages/sagenb/data/jquery/plugins/../../../../../../../share/javascript/jquery-form