/basic · sink: flask.render_template_string
User input rendered as a Flask template. Full Jinja2 evaluation.
render_template_string runs your input through Flask's full Jinja2 environment. Try {{ 7*7 }} to confirm template evaluation, then {{ config['VULNLAB_SSTI_BASIC'] }} to read the lab flag, then walk ''.__class__.__mro__[1].__subclasses__() for RCE.