Using Jinja2 templates without autoescaping enabled leaves application vulnerable to [XSS attacks](https://owasp.org/www-project-top-ten/2017/A72017-Cross-SiteScripting_(XSS).

Autoescaping is the concept of automatically escaping special characters. Special characters for HTML, XML and XHTMl are &, >, <, " as well as '. These characters carry specific meanings so need to be replaced by so called entities if you want to use them for text. Not doing so makes application susceptible to Cross Site Scripting (XSS) attacks.

When configuring the Jinja2 environment, the option to use autoescaping on input can be specified. By default, autoescaping is disabled. When enabled, Jinja2 will filter input strings to escape any HTML content submitted via template variables.

Bad practice

from jinja2 import Environment

template_env1 = Environment() # Insecure. Autoescape set to False by default
template_env2 = Environment(autoescape=False) # Insecure

Recommended

from jinja2 import Environment

template_env = Environment(autoescape=True) # Secure

References:

Autoescaping in Jinja
OWASP Top 10 2021 Category A03 - Injection
OWASP Top 10 2021 Category A06 - Vulnerable and Outdated Components
SANS Top 25
CWE 79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

sanketsaurav / lore

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