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78 lines
2.8 KiB
Markdown
78 lines
2.8 KiB
Markdown
# Email Injections
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## Email Header Injection
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## Inject Cc and Bcc after sender argument
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```
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From:sender@domain.com%0ACc:recipient@domain.co,%0ABcc:recipient1@domain.com
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```
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The message will be sent to the recipient and recipient1 accounts.
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## Inject argument
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```
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From:sender@domain.com%0ATo:attacker@domain.com
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```
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The message will be sent to the original recipient and the attacker account.
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## Inject Subject argument
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```
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From:sender@domain.com%0ASubject:This is%20Fake%20Subject
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```
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The fake subject will be added to the original subject and in some cases will replace it. It depends on the mail service behavior.
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## Change the body of the message
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Inject a two-line feed, then write your message to change the body of the message.
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```
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From:sender@domain.com%0A%0AMy%20New%20%0Fake%20Message.
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```
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## PHP mail() function exploitation
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```bash
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# The function has the following definition:
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php --rf mail
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Function [ <internal:standard> function mail ] {
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- Parameters [5] {
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Parameter #0 [ <required> $to ]
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Parameter #1 [ <required> $subject ]
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Parameter #2 [ <required> $message ]
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Parameter #3 [ <optional> $additional_headers ]
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Parameter #4 [ <optional> $additional_parameters ]
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}
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}
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```
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### The 5th parameter ($additional\_parameters)
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This section is going to be based on **how to abuse this parameter supposing that an attacker controls it**.
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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)`.
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An attacker can **inject extract parameters for sendmail** in this case.
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#### Differences in the implementation of /usr/sbin/sendmail
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**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.
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Here are a few examples of different man pages of sendmail command/interface:
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* Sendmail MTA: http://www.sendmail.org/\~ca/email/man/sendmail.html
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* Postfix MTA: http://www.postfix.org/mailq.1.html
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* Exim MTA: https://linux.die.net/man/8/eximReferences
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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)
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## References
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* [**https://resources.infosecinstitute.com/email-injection/**](https://resources.infosecinstitute.com/email-injection/)
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* [**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)
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