testing-for-email-header-injection

name	testing-for-email-header-injection
description	Test web application email functionality for SMTP header injection vulnerabilities that allow attackers to inject additional email headers, modify recipients, and abuse contact forms for spam relay. Use when testing web application email functionality for smtp header injection vulnerabilities.
domain	cybersecurity
tags	["email-injection","smtp-injection","crlf-injection","header-injection","spam-relay","contact-form","email-security"]
subdomain	web-application-security
version	1.0
author	oyi77
license	Apache-2.0
nist_csf	["PR.PS-01","ID.RA-01","PR.DS-10","DE.CM-01"]

Testing For Email Header Injection

Overview

Cybersecurity skill for testing for email header injection. Follows industry best practices and security standards.

When to Use

Trigger phrases:

• "testing for email header injection"

• "When testing contact forms, feedback forms, or "email a friend" functionality"

• "During assessment of password reset email functionality"

• "When testing newsletter subscription or notification email systems"

• When testing contact forms, feedback forms, or "email a friend" functionality

• During assessment of password reset email functionality

• When testing newsletter subscription or notification email systems

• During penetration testing of applications that send emails based on user input

• When auditing email-related API endpoints for header injection

When NOT to Use

• When you lack proper authorization for testing
• For production systems without change management
• When the task requires legal or compliance expertise beyond technical scope

Prerequisites

• Burp Suite for intercepting and modifying HTTP requests
• Understanding of SMTP protocol and email header structure
• Knowledge of CRLF injection techniques (\r\n sequences)
• Test email accounts for receiving injected emails
• Access to application features that trigger email sending
• SMTP server logs access for monitoring injection attempts

Workflow

# Example: IOC detection
import re

IOC_PATTERNS = {
    "ip": r"\b(?:\d{1,3}\.){3}\d{1,3}\b",
    "domain": r"\b[a-z0-9-]+\.[a-z]{2,}\b",
    "hash_md5": r"\b[a-f0-9]{32}\b",
    "hash_sha256": r"\b[a-f0-9]{64}\b",
}

def extract_iocs(text: str) -> dict:
    return {k: re.findall(v, text)  k, v  IOC_PATTERNS.items()}