Sending emails is security-sensitive and can expose an application to a large range of vulnerabilities.
Information Exposure
Emails often contain sensitive information which might be exposed to an attacker if he can add an arbitrary address to the recipient list.
Spamming / Phishing
Malicious user can abuse email based feature to send spam or phishing content.
Dangerous Content Injection
Emails can contain HTML and JavaScript code, thus they can be used for XSS attacks.
Email Headers Injection
Email fields such as subject, to, cc, bcc, from are set in email "headers".
Using unvalidated user input to set those fields might allow attackers to inject new line characters in headers to craft malformed SMTP requests.
Although modern libraries are filtering new line character by default, user data used in email "headers" should always be validated.
In the past, it has led to the following vulnerabilities:
You are at risk if you answered yes to any of those questions.
smtplib
import smtplib
def send(from_email, to_email, msg):
server = smtplib.SMTP('localhost', 1025)
server.sendmail(from_email, to_email, msg) # Sensitive
Django
from django.core.mail import send_mail def send(subject, msg, from_email, to_email): send_mail(subject, msg, from_email, [to_email]) # Sensitive
Flask-Mail
from flask import Flask
from flask_mail import Mail, Message
app = Flask(__name__)
def send(subject, msg, from_email, to_email):
mail = Mail(app)
msg = Message(subject, [to_email], body, sender=from_email)
mail.send(msg) # Sensitive{code}
This rule is deprecated, and will eventually be removed.