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**Note:** A [p0wny-shell](https://github.com/flozz/p0wny-shell/blob/master/shell.php) php webshell can **automatically** check and bypass the following function if some of them be disabled.
**mail / mb\_send\_mail** - This function is used to send mails, but it can also be abused to inject arbitrary commands inside the `$options` parameter. This is because **php `mail` function** usually call `sendmail` binary inside the system and it allows you to **put extra options**. However, you won't be able to see the output of the executed command, so it's recommended to create shell script that writes the output to a file, execute it using mail, and print the output:
**dl** - This function can be used to dynamically load a PHP extension. This function won't be present always, so you should check if it's available before trying to exploit it. Read[ this page to learn how to exploit this function](disable\_functions-bypass-dl-function.md).
Apart from eval there are other ways to execute PHP code: include/require can be used for remote code execution in the form of Local File Include and Remote File Include vulnerabilities.
```php
${<phpcode>} // If your input gets reflected in any PHP string, it will be executed.
eval()
assert() // identical to eval()
preg_replace('/.*/e',...) // e does an eval() on the match
create_function() // Create a function and use eval()
include()
include_once()
require()
require_once()
$_GET['func_name']($_GET['argument']);
$func = new ReflectionFunction($_GET['func_name']);
**Disabled functions** is the setting that can be configured in `.ini` files in PHP that will **forbid** the use of the indicated **functions**. **Open basedir** is the setting that indicates to PHP the folder that it can access.\
`open_basedir` will configure the folders that PHP can access, you **won't be able to to write/read/execute any file outside** those folders, but also you **won't even be able to list** other directories.\
However, if somehow you are able to execute arbitrary PHP code you can **try** the following chunk of **codes** to try to **bypass** the restriction.
Note that the first thing you need to do is find where is the **unix socket of php-fpm**. It use to be under `/var/run` so you can **use the previous code to list the directory and find it**.\
This scripts will communicate with **unix socket of php-fpm** (usually located in /var/run if fpm is used) to execute arbitrary code. The `open_basedir` settings will be overwritten by the **PHP\_VALUE** attribute that is sent.\
Also note the **commented line 324**, you can uncomment it and the **payload will automatically connect to the given URL and execute the PHP code** contained there.\
You may be thinking that just in the same way we have overwritten `open_basedir` configuration we can **overwrite `disable_functions`**. Well, try it, but it won't work, apparently **`disable_functions` can only be configured in a `.ini` php** configuration file and the changes you perform using PHP\_VALUE won't be effective on this specific setting.
If you manage have PHP code executing inside a machine you probably want to go to the next level and **execute arbitrary system commands**. In this situation is usual to discover that most or all the PHP **functions** that allow to **execute system commands have been disabled** in **`disable_functions`.**\
You can use the tool [https://github.com/teambi0s/dfunc-bypasser](https://github.com/teambi0s/dfunc-bypasser) and it will indicate you which function (if any) you can use to **bypass****`disable_functions`**.
Just return to the beginning of this page and **check if any of the command executing functions isn't disabled and available in the environment**. If you find just 1 of them, you will be able to use it to execute arbitrary system commands.
It's well known that some functions in PHP like `mail()`are going to **execute binaries inside the system**. Therefore, you can abuse them using the environment variable `LD_PRELOAD` to make them load an arbitrary library that can execute anything.
* **`mb_send_mail`**: Effective when the `php-mbstring` module is installed.
* **`imap_mail`**: Works if `php-imap` module is present.
* **`libvirt_connect`**: Requires the `php-libvirt-php` module.
* **`gnupg_init`**: Utilizable with the `php-gnupg` module installed.
* **`new imagick()`**: This class can be abused to bypass restrictions. Detailed exploitation techniques can be found in a comprehensive [**writeup here**](https://blog.bi0s.in/2019/10/23/Web/BSidesDelhi19-evalme/).
In order to abuse this misconfiguration you can [**Chankro**](https://github.com/TarlogicSecurity/Chankro). This is a tool that will **generate a PHP exploit** that you need to upload to the vulnerable server and execute it (access it via web).\
**Chankro** will write inside the victims disc the **library and the reverse shell** you want to execute and will use the\*\*`LD_PRELOAD` trick + PHP `mail()`\*\* function to execute the reverse shell.
In the following example you can see how to **create a chankro exploit** for **arch 64**, that will execute `whoami` and save the out in _/tmp/chankro\_shell.out_, chankro will **write the library and the payload** in _/tmp_ and the **final exploit** is going to be called **bicho.php** (that's the file you need to upload to the victims server):
If you find that **mail** function is blocked by disabled functions, you may still be able to use the function **mb\_send\_mail.**\
More information about this technique and Chankro here: [https://www.tarlogic.com/en/blog/how-to-bypass-disable\_functions-and-open\_basedir/](https://www.tarlogic.com/en/blog/how-to-bypass-disable\_functions-and-open\_basedir/)
I have created a webshell that makes very easy to perform this actions (note that most webshells will offer you this options also): [https://github.com/carlospolop/phpwebshelllimited](https://github.com/carlospolop/phpwebshelllimited)
These functions accept a string parameter which could be used to call a function of the attacker's choice. Depending on the function the attacker may or may not have the ability to pass a parameter. In that case an Information Disclosure function like phpinfo() could be used.
Most of these function calls are not sinks. But rather it maybe a vulnerability if any of the data returned is viewable to an attacker. If an attacker can see phpinfo() it is definitely a vulnerability.
extract // Opens the door for register_globals attacks (see study in scarlet).
parse_str // works like extract if only one argument is given.
putenv
ini_set
mail // has CRLF injection in the 3rd parameter, opens the door for spam.
header // on old systems CRLF injection could be used for xss or other purposes, now it is still a problem if they do a header("location: ..."); and they do not die();. The script keeps executing after a call to header(), and will still print output normally. This is nasty if you are trying to protect an administrative area.
According to RATS all filesystem functions in php are nasty. Some of these don't seem very useful to the attacker. Others are more useful than you might think. For instance if allow\_url\_fopen=On then a url can be used as a file path, so a call to copy($\_GET\['s'], $\_GET\['d']); can be used to upload a PHP script anywhere on the system. Also if a site is vulnerable to a request send via GET everyone of those file system functions can be abused to channel and attack to another host through your server.
<summary><strong>Learn AWS hacking from zero to hero with</strong><ahref="https://training.hacktricks.xyz/courses/arte"><strong>htARTE (HackTricks AWS Red Team Expert)</strong></a><strong>!</strong></summary>
* If you want to see your **company advertised in HackTricks** or **download HackTricks in PDF** Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@carlospolopm**](https://twitter.com/hacktricks_live)**.**
* **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.
