Change the extensions to a less common extension, such as file.php5, file.shtml, file.asa, file.jsp, file.jspx, file.aspx, file.asp, file.phtml, file.cshtml.Change the value of Content-Type as image/jpeg in HTTP request.If the filtering is performed on the server-side, then various techniques can be attempted to bypass it, including: If the restrictions are performed on the client-side using JavaScript, then they can be trivially bypassed with an intercepting proxy. The first step is to determine what the filters are allowing or blocking, and where they are implemented. Once the shell is uploaded (with a random name), you can execute operating system commands by passing them in the cmd GET parameter: ![]() The example below shows a simple PHP based shell, that executes operating system commands passed to it in a GET parameter, and can only be accessed from a specific IP address: Remember to remove the shell when you are done. Implementing IP based restrictions on the shell.Uploading the shell with a randomly generated name.A number of techniques can be used to protect the shell from unauthorised access, such as: Uploading this kind of shell onto an internet facing server is dangerous, because it allows anyone who knows (or guesses) the location of the shell to execute code on the server. In order for this attack to be successful, the file needs to be uploaded inside the webroot, and the server must be configured to execute the code. If the server is configured to execute code, then it may be possible to obtain command execution on the server by uploading a file known as a web shell, which allows you to execute arbitrary code or operating system commands. The simplest checks that an application can do are to determine that only trusted types of files can be uploaded. Try to upload the malicious files to the application and determine whether it is accepted and processed.Obtain or create a set of malicious files for testing.Determine how the uploaded files are processed.If documentation is not available then consider what would be appropriate based on the purpose of the application.Review the project documentation to identify what file types are considered acceptable, and what types would be considered dangerous or malicious.Identify the file upload functionality.While these are considered safe, if an attacker is able to upload executable code (such as a PHP script), this could allow them to execute operating system commands, read and modify information in the filesystem, access the backend database and fully compromise the server. ![]() ExampleĪ common example of this vulnerability is an application such as a blog or forum that allows users to upload images and other media files. Malicious files could be detected and stopped at various points of the application architecture such as: Intrusion Detection/Prevention System, application server anti-virus software or anti-virus scanning by application as files are uploaded (perhaps offloading the scanning using SCAP). The application may allow the upload of malicious files that include exploits or shellcode without submitting them to malicious file scanning. ![]() Additionally, this is different from uploading unexpected files in that while the file type may be accepted the file may still be malicious to the system.įinally, “malicious” means different things to different systems, for example malicious files that may exploit SQL server vulnerabilities may not be considered as “malicious” in an environment using a NoSQL data store. Vulnerabilities related to the uploading of malicious files is unique in that these “malicious” files can easily be rejected through including business logic that will scan files during the upload process and reject those perceived as malicious. Although many sites implement simple restrictions based on a list of permitted (or blocked) extensions, this is not sufficient to prevent attackers from uploading legitimate file types that have malicious contents. Although input validation is widely understood for text-based input fields, it is more complicated to implement when files are accepted. Many application’s business processes allow users to upload data to them. Home > Latest > 4-Web Application Security Testing > 10-Business Logic Testing Test Upload of Malicious Files ID
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |