PHP-Fusion 9.03.50 - Cross Site Scripting

# Exploit Title: PHPFusion 9.03.50 - Persistent Cross-Site Scripting
# Date: 2020-05-20
# Exploit Author: coiffeur
# Vendor Homepage: https://www.php-fusion.co.uk/home.php
# Software Link: https://www.php-fusion.co.uk/php_fusion_9_downloads.php
# Version: v9.03.50

## How?

When creating a thread or editing one of his messages with HTML content, it turns out that the injected characters are correctly escaped as it can be seen when I tried here to fuzz the message field with the string `i<3"'ivoire`.

https://therealcoiffeur.github.io/captures/c5_1.png

https://therealcoiffeur.github.io/captures/c5_2.png

https://therealcoiffeur.github.io/captures/c5_3.png

It's when I became interested in the print feature that things turned out to be interesting. Indeed, the print function allows you to simplify the page as much as possible so that it contains only text. So the print function returns all messages in text format so that the content of a thread can be easily printed (in order to generate this result it is necessary to click on the button circled in blue in figure 3). 

![alt text](../captures/c5_4.png "Figure 5: Injection of HTML character (part 3)")

![alt text](../captures/c5_5.png "Figure 6: Injection of HTML character (part 3)")

Once the page is generated by the print functionality we realize by analyzing the body of the server response, that our characters are no longer sanitized.

Now we just have to create a message that will allow us to execute JavaScript by replacing the contents of the previous message with:

```html
<img onerror="alert(1)" src=xxx>
```

https://therealcoiffeur.github.io/captures/c5_4.png

https://therealcoiffeur.github.io/captures/c5_5.png

## Why?

The route requested to generate this result is the route <span style="color:red">\<ROOT\>/print.php?type=F&item_id=1&rowstart=0</span>. It is thus page <span style="color:red">\<ROOT\>/print.php</span> which is called, with the following parameters:

```
$_GET array (size=3)
    'type' => string 'F' (length=1)
    'item_id' => string '1' (length=1)
    'rowstart' => string '0' (length=1)
```

File: <span style="color:red">\<ROOT\>/print.php</span>
```php

...

case "F":
    ...

    echo parse_textarea($data['post_message']);

    ...

```


File: <span style="color:red">\<ROOT\>/includes/core_functions_include.php</span>
```php
function parse_textarea($text, $smileys = TRUE, $bbcode = TRUE, $decode = TRUE, $default_image_folder = IMAGES, $add_line_breaks = FALSE, $descript = TRUE) {
    $text = $decode == TRUE ? html_entity_decode(stripslashes($text), ENT_QUOTES, fusion_get_locale('charset')) : $text;
    $text = $decode == TRUE ? html_entity_decode($text, ENT_QUOTES, fusion_get_locale('charset')) : $text; // decode for double encoding.
    $text = !empty($default_image_folder) ? parse_imageDir($text, $default_image_folder) : $text;
    $text = $smileys == TRUE ? parsesmileys($text) : $text;
    $text = $bbcode == TRUE ? parseubb($text) : $text;
    $text = fusion_parse_user($text);
    $text = $add_line_breaks ? nl2br($text) : $text;
    $text = $descript == TRUE ? descript($text) : $text;

    return (string)$text;
}
```

As you can see by reading the function code of `parse_textarea()`, the text is not sanitized, which leads to the Stored XSS.