Python SSTI is common because Flask ships Jinja2 and render_template_string is frequently fed user input. The two engines here differ sharply in how hard RCE is.

Jinja2 restricts direct attribute access in its sandboxed mode but exposes a rich object graph, so exploitation is about walking from an exposed object to the Python runtime. Mako places no such restriction: it evaluates Python directly inside ${ ... }, so RCE is immediate. Detection for both starts with {{7*7}} (Jinja2) or ${7*7} (Mako) returning 49.

Engines#

• Jinja2: object-graph walks (cycler, config, lipsum) to os, and sandbox escape.
• Mako: direct Python evaluation in ${ } and <% %> blocks.

References#

• Jinja2 and Mako documentation (sandboxing, expression syntax)
• PortSwigger Web Security Academy: Server-side template injection