
== Why is this an issue?

include::../rationale.adoc[]

include::../impact.adoc[]

== How to fix it

=== Code examples

==== Noncompliant code example

The following code is vulnerable to server-side template injection because it
is inserting untrusted inputs into a string that is then processed for
rendering. +
This vulnerability arises because the rendering function does not validate the
input, allowing attackers to potentially inject malicious Python code for
execution.

[source,python,diff-id=1,diff-type=noncompliant]
----
from flask import request, render_template_string

@app.route('/example')
def example():
    username = request.args.get('username')
    template = f"<p>Hello {username}</p>"
    return render_template_string(template) # Noncompliant
----

==== Compliant solution

[source,python,diff-id=1,diff-type=compliant]
----
from flask import request, render_template_string

@app.route('/example')
def example():
    username = request.args.get('username')
    template = "<p>Hello {{ username }}</p>"
    return render_template_string(template, username=username)
----

=== How does this work?

==== Use template variables

The universal method to prevent path injection is to sanitize untrusted data.
Manual sanitization is error-prone, so it is best to automate the process.

Here, `render_template_string` automatically sanitizes template variables by
escaping them. This means that any untrusted data will not be able to break out
of the initially intended template logic.

== Resources

=== Articles & blog posts

* https://medium.com/@nyomanpradipta120/ssti-in-flask-jinja2-20b068fdaeee[SSTI in Flask/Jinja2]

include::../standards.adoc[]


ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

include::../message.adoc[]

=== Highlighting

"[varname]" is tainted (assignments and parameters)

this argument is tainted (method invocations)

the returned value is tainted (returns & method invocations results)

'''
endif::env-github,rspecator-view[]
