hacktricks/emails-vulns.md

# Emails Vulnerabilities

## Payloads

### Ignored parts of an email

The symbols: **+, -** and **{} **in rare occasions can be used for tagging and ignored by most e-mail servers

* E.g. john.doe+intigriti@example.com → john.doe@example.com

**Comments between parentheses () **at the beginning or the end will also be ignored 

* E.g. john.doe(intigriti)@example.com → john.doe@example.com

### Whitelist bypass

* inti(;inti@inti.io;)@whitelisted.com
* inti@inti.io(@whitelisted.com)
* inti+(@whitelisted.com;)@inti.io

### IPs

You can also use IPs as domain named between square brackets:

* john.doe@\[127.0.0.1]
* john.doe@\[IPv6:2001:db8::1]

### Other vulns

![](<.gitbook/assets/image (296).png>)

## Third party SSO

### XSS

Some services like **github **or **salesforce allows **you to create an **email address with XSS payloads on it**. If you can **use this providers to login on other services** and this services** aren't sanitising** correctly the email, you could cause **XSS**.

### Account-Takeover

If a **SSO service** allows you to **create an account without verifying the given email address** (like **salesforce**) and then you can use that account to **login in a different service** that **trusts **salesforce, you could access any account.\
_Note that salesforce indicates if the given email was or not verified but so the application should take into account this info._

## Reply-To

You can send an email using _**From: company.com**_** **and _**Replay-To: attacker.com **_and if any **automatic reply **is sent due to the email was sent **from **an **internal address **the **attacker **may be able to **receive **that **response**.

## **References**

* ****[**https://drive.google.com/file/d/1iKL6wbp3yYwOmxEtAg1jEmuOf8RM8ty9/view**](https://drive.google.com/file/d/1iKL6wbp3yYwOmxEtAg1jEmuOf8RM8ty9/view)****

## Hard Bounce Rate

Some applications like AWS have a **Hard Bounce Rate** (in AWS is 10%), that whenever is overloaded the email service is blocked.

A **hard bounce** is an **email** that couldn’t be delivered for some permanent reasons. Maybe the **email’s** a fake address, maybe the **email** domain isn’t a real domain, or maybe the **email** recipient’s server won’t accept **emails**) , that means from total of 1000 emails if 100 of them were fake or were invalid that caused all of them to bounce, **AWS SES **will block your service.

So, if you are able to **send mails (maybe invitations) from the web application to any email address, you could provoke this block by sending hundreds of invitations to nonexistent users and domains: Email service DoS.**