File Signature Shenanigans: Tricking Servers with Crafty Uploads (part two)

[D2]

I have nothing to do, so I'll help you solve the DVWA impossible challenge.

If we analyze the code....

PHP: Скопировать в буфер обмена

<?php

if( isset( $_POST[ 'Upload' ] ) ) {
    // Check Anti-CSRF token
    checkToken( $_REQUEST[ 'user_token' ], $_SESSION[ 'session_token' ], 'index.php' );


    // File information
    $uploaded_name = $_FILES[ 'uploaded' ][ 'name' ];
    $uploaded_ext  = substr( $uploaded_name, strrpos( $uploaded_name, '.' ) + 1);
    $uploaded_size = $_FILES[ 'uploaded' ][ 'size' ];
    $uploaded_type = $_FILES[ 'uploaded' ][ 'type' ];
    $uploaded_tmp  = $_FILES[ 'uploaded' ][ 'tmp_name' ];

    // Where are we going to be writing to?
    $target_path   = DVWA_WEB_PAGE_TO_ROOT . 'hackable/uploads/';
    //$target_file   = basename( $uploaded_name, '.' . $uploaded_ext ) . '-';
    $target_file   =  md5( uniqid() . $uploaded_name ) . '.' . $uploaded_ext;
    $temp_file     = ( ( ini_get( 'upload_tmp_dir' ) == '' ) ? ( sys_get_temp_dir() ) : ( ini_get( 'upload_tmp_dir' ) ) );
    $temp_file    .= DIRECTORY_SEPARATOR . md5( uniqid() . $uploaded_name ) . '.' . $uploaded_ext;

    // Is it an image?
    if( ( strtolower( $uploaded_ext ) == 'jpg' || strtolower( $uploaded_ext ) == 'jpeg' || strtolower( $uploaded_ext ) == 'png' ) &&
        ( $uploaded_size < 100000 ) &&
        ( $uploaded_type == 'image/jpeg' || $uploaded_type == 'image/png' ) &&
        getimagesize( $uploaded_tmp ) ) {

        // Strip any metadata, by re-encoding image (Note, using php-Imagick is recommended over php-GD)
        if( $uploaded_type == 'image/jpeg' ) {
            $img = imagecreatefromjpeg( $uploaded_tmp );
            imagejpeg( $img, $temp_file, 100);
        }
        else {
            $img = imagecreatefrompng( $uploaded_tmp );
            imagepng( $img, $temp_file, 9);
        }
        imagedestroy( $img );

        // Can we move the file to the web root from the temp folder?
        if( rename( $temp_file, ( getcwd() . DIRECTORY_SEPARATOR . $target_path . $target_file ) ) ) {
            // Yes!
            echo "<pre><a href='${target_path}${target_file}'>${target_file}</a> succesfully uploaded!</pre>";
        }
        else {
            // No
            echo '<pre>Your image was not uploaded.</pre>';
        }

        // Delete any temp files
        if( file_exists( $temp_file ) )
            unlink( $temp_file );
    }
    else {
        // Invalid file
        echo '<pre>Your image was not uploaded. We can only accept JPEG or PNG images.</pre>';
    }
}

// Generate Anti-CSRF token
generateSessionToken();

?>

you can see that the code checks for file extensions and types, it doesn't properly validate them.
We can bypass this by manipulating the Content-Type header in the HTTP request.

The code generates a unique filename using md5( uniqid() . $uploaded_name ), but it still retains the original file extension.
We can abuse this to upload PHP files disguised as other file types.
to exploit this we need to:

1 Craft the Payload

• Use your favorite text editor to create a PHP file with your malicious code. Let's call it evil.php.
• Inside evil.php, put your PHP code to execute commands or do whatever nefarious deeds you want.

2 Bypass File Type Validation

• Rename evil.php to something harmless, like innocent.jpg. This fools the server into thinking it's just a harmless image file.

3 Set Up Your Attacker Machine

• You'll need a tool to manipulate HTTP requests. Let's use curl for this example. If you don't have it, install it.
• Open a terminal and navigate to the directory where innocent.jpg (formerly evil.php) is located.

4 Craft the HTTP Request

Use curl to craft the HTTP request. Here's an example command:

curl -X POST -F "uploaded=@innocent.jpg" -F "Upload=Upload" -F "user_token=<your_csrf_token_or_whatever>" <target_url>
Нажмите, чтобы раскрыть...

Replace <your_csrf_token> with the CSRF token you obtained somehow (if there is no csrf token ignore that part )and <target_url> with the URL of the vulnerable file upload page.

5 Send the Evil File

• Execute the curl command in your terminal. This sends the HTTP request with your disguised evil PHP shell to the vulnerable server.

6 Access the Shell

• Once the server accepts the upload, navigate to the upload directory on the server where innocent.jpg was uploaded.
• In your web browser, visit the URL of innocent.jpg. This executes your evil PHP code, giving you access to the server. ( don't forget the lfi trick).

7 Exploiting the System:

• Now that you have access to the server through your shell, you can run commands, access files, or do whatever mischief you please.

Author: Att4ck A.K.A Iwakura​

erm pls don't just read and leave. hit the like button i need some reactions lol.