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Email spoofing

Need​

Implementation of DMARC (Domain-based Message Authentication, Reporting, and Conformance) records

Context​

  • Usage of Go 1.16 for building high-performance and scalable applications
  • Usage of Gin framework for building web applications in Go

Description​

Non compliant code​

package main

import (
	"github.com/gin-gonic/gin"
	"net/http"
)

func main() {
	r := gin.Default()
	r.POST("/sendEmail", func(c *gin.Context) {
		var emailData EmailData
		if err := c.ShouldBindJSON(&emailData); err != nil {
			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
			return
		}
		sendEmail(emailData)
		c.JSON(http.StatusOK, gin.H{"status": "Email sent"})
	})
	r.Run()
}

type EmailData struct {
	From    string `json:"from"`
	To      string `json:"to"`
	Subject string `json:"subject"`
	Body    string `json:"body"`
}

func sendEmail(emailData EmailData) {
	// Code for sending email
}

The above code is a simple email sending API endpoint using the Gin framework in Go.

When a POST request is made to the /sendEmail endpoint, the emailData object is parsed from the request body. This object contains the From, To, Subject, and Body of the email.

The parsed emailData is then passed to the sendEmail function, which handles the process of sending the email.

The vulnerability in this code lies in the fact that there is no verification of the From field in the emailData. This means that an attacker could potentially spoof the From field, making it appear as if the email was sent from a different email address.

In addition, the absence of Domain-based Message Authentication, Reporting & Conformance (DMARC) records in the email sending process means that email receivers cannot verify whether the email was legitimately sent from the purported email domain. This could potentially allow an attacker to spoof the email domain, making it appear as if the email was sent from a different domain.

To fix this vulnerability, it is recommended to implement DMARC records in the email sending process to prevent email domain spoofing. Also, the From field in the emailData should be verified to ensure that it matches the authenticated user's email address.

Steps​

  • Implement DMARC (Domain-based Message Authentication, Reporting, and Conformance) records for the email domain.
  • Configure DMARC policy to reject or quarantine emails that fail authentication.
  • Enable SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) to authenticate outgoing emails.
  • Validate and sanitize user input for the 'from' field to prevent email spoofing.
  • Implement email validation checks to ensure that the 'from' field matches the authenticated user.
  • Consider implementing additional email security measures such as email encryption and email authentication protocols like DMARC, SPF, and DKIM.
  • Regularly update and patch the email sending library or service used in the 'sendEmail' function to address any security vulnerabilities.

Compliant code​

package main

import (
	"github.com/gin-gonic/gin"
	"net/http"
	"net/mail"
)

func main() {
	r := gin.Default()
	r.POST("/sendEmail", func(c *gin.Context) {
		var emailData EmailData
		if err := c.ShouldBindJSON(&emailData); err != nil {
			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
			return
		}
		if err := validateEmail(emailData.From); err != nil {
			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
			return
		}
		sendEmail(emailData)
		c.JSON(http.StatusOK, gin.H{"status": "Email sent"})
	})
	r.Run()
}

type EmailData struct {
	From    string `json:"from"`
	To      string `json:"to"`
	Subject string `json:"subject"`
	Body    string `json:"body"`
}

func validateEmail(email string) error {
	_, err := mail.ParseAddress(email)
	return err
}

func sendEmail(emailData EmailData) {
	// Code for sending email
}

The updated code includes a function validateEmail that validates the 'from' field of the email. This function uses the mail.ParseAddress function from the Go standard library to parse the email address. If the email address is not valid, it returns an error.

In the main function, after binding the JSON data to the emailData struct, it calls the validateEmail function to validate the 'from' field of the email. If the email is not valid, it returns a 400 Bad Request status with an error message.

Please note that this code only validates the format of the email address. It does not authenticate the email address or prevent email spoofing. To prevent email spoofing, you should implement DMARC (Domain-based Message Authentication, Reporting, and Conformance) records for your email domain. You should also enable SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) to authenticate outgoing emails.

In addition, you should configure your DMARC policy to reject or quarantine emails that fail authentication. You should also consider implementing additional email security measures such as email encryption.

Finally, you should regularly update and patch the email sending library or service used in the 'sendEmail' function to address any security vulnerabilities.

References​

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