Original Post: How to prevent HTML email injection in Python web apps
tl;dr:
- HTML Injection Vulnerability: When user input is rendered as HTML in emails, it can lead to phishing attacks. Attackers can exploit vulnerabilities to make emails appear to come from legitimate sources.
- Flask Defaults Issue: Flask only escapes templates with specific file extensions, leading to potential HTML injection if the template isn’t properly escaped.
- Detection & Prevention: Methods to detect and prevent HTML injection in code are available.
Summary:
HTML injection vulnerabilities can affect emails formatted with HTML, allowing an attacker to insert malicious HTML or scripts. This is particularly risky in web apps built with frameworks like Flask and Django, where subtle mishandling of user input can lead to security issues.
For example, in Flask, if an email template file doesn’t have the .html extension, Flask won’t automatically escape HTML content. This can be exploited if user data is injected into these templates, leading to phishing attempts using legitimate email addresses.
Prevention Tips:
- Ensure all email templates are properly escaped, particularly by using recognized extensions like
.html. - Use automated tools like Semgrep to scan for security issues in code.
- Consider opting for plain text emails if security is a major concern.
- For HTML emails, use templating engines that automatically escape user input.
By following these practices, developers can mitigate the risk of HTML injection and protect users from phishing attacks.
Go here to read the Original Post