== How to fix it in Python Standard Library

=== Code examples

The following code is vulnerable to SSRF as it opens a URL defined by untrusted data.

==== Noncompliant code example

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

@app.route('/example')
def example():
    url = request.args["url"]
    urlopen(url).read() # Noncompliant
----

==== Compliant solution

[source,python,diff-id=1,diff-type=compliant]
----
from flask import request
from urllib.parse import urlparse
from urllib.request import urlopen

SCHEMES_ALLOWLIST = ['https']
DOMAINS_ALLOWLIST = ['trusted1.example.com', 'trusted2.example.com']

@app.route('/example')
def example():
    url = request.args["url"]
    if urlparse(url).hostname in DOMAINS_ALLOWLIST and urlparse(url).scheme in SCHEMES_ALLOWLIST:
        urlopen(url).read()
----

include::../../common/fix/how-does-this-work.adoc[]

The compliant code example uses such an approach.

=== Pitfalls

include::../../common/pitfalls/starts-with.adoc[]
