Possible file upload attack

A detailed vulnerability analysis along with the exploitation for these issues is available here. CVE— — Insufficient shell characters filtering leading to potentially remote code execution.

To check for this issue, one can follow the below steps [Assuming the ImageMagick Library is in use]:. At the back, the ImageMagick library will try to process the file by running convert exploit. Similarly, the other vulnerabilities can also be exploited and a great explanation is available here. Stay tuned for Part-2 of the File Upload attack series for more interesting attack vectors. Happy Hacking! Vulnerability Coordination through CrowdSourced Security. Reading Time 7 min. Remote Code Execution One of the most interesting attacks that come into mind whenever there is a file upload functionality is Remote Code Execution.

In order to achieve remote code execution, one can try the following steps: Create a PHP shell or use an existing shell. Unrestricted File Upload ZipSlip Attack ZipSlip attack is an interesting attack vector that can be tested when the application accepts archives in file upload functionality and later unarchive it for further processing. File Overwrite Attack File overwrite is an interesting attack during the file upload when a user can control and arbitrarily set the path where the file should be stored.

Path Traversal Attack This attack may look similar to the attack mentioned above, i. To check for this issue, one can follow below simple steps: Navigate to the file upload functionality and upload a file while capturing the request with Burp Suite.

To check for this issue, one can follow below simple steps: Create a file that is larger in the size than defined upper limit. For example, an image file having a MB file size. These are generally provided by the transport, such as HTTP multi-part encoding. This data may trick the application into overwriting a critical file or storing the file in a bad location.

You must validate the metadata extremely carefully before using it. The other class of problem is with the file size or content. The range of problems here depends entirely on what the file is used for. See the examples below for some ideas about how files might be misused.

To protect against this type of attack, you should analyse everything your application does with files and think carefully about what processing and interpreters are involved. If the service is up an running with the Insecure Configuration, any one can beat the getimagesize function by writing comments in GIF file. There are two basic kinds of file upload vulnerabilities.

We are going to give these descriptive names in this article that you may not have heard elsewhere, but we feel these describe the difference between the basic types of upload vulnerability. A local file upload vulnerability is a vulnerability where an application allows a user to upload a malicious file directly which is then executed.

A remote file upload vulnerability is a vulnerability where an application uses user input to fetch a remote file from a site on the Internet and store it locally. This file is then executed by an attacker. Lets look at each of these vulnerabilities in some detail, how they are created and how to avoid them. Here is the code that created the vulnerability:. Mistake 1: There is no authentication or authorization check to make sure that the user has signed in authentication and has access to perform a file upload authorization.

This allows an attacker to upload a file to the website without needing to sign-in or to have the correct permissions. As a developer, you can avoid this mistake by verifying the user has permissions to upload files before processing the file upload:. Mistake 2: There is no sanitization on the file name or contents. This allows an attacker to upload a file with a. Developers can avoid this mistake by sanitizing the file name so that it does not contain an extension that can execute code via the web server.

WordPress has some built-in functions to check and sanitize files before uploading. You can also further limit what is allowed by specifying the mime types allowed.

This list allows only images. When receiving an upload, you can avoid attackers uploading executable PHP or other code by examining your uploads for content. For example, if you are accepting image uploads, call the PHP getimagesize function on the uploaded file to determine if it is a valid image.

A remote file upload vulnerability is when an application does not accept uploads directly from site visitors. Instead, a visitor can provide a URL on the web that the application will use to fetch a file.