.. change::
    :tags: bug, template
    :tickets: 434

    Fixed issue in :class:`.TemplateLookup` where a URI with a double-slash
    prefix (e.g. ``//../../``) could bypass the directory traversal check in
    :class:`.Template`, allowing reads of arbitrary files outside of the
    template directory. The issue was caused by an inconsistency in how leading
    slashes were stripped between :meth:`.TemplateLookup.get_template` and
    :class:`.Template` initialization.
