Testing web applications is a standard task for every security analyst. Various automated and semi-automated security testing tools exist to simplify the task. HTTP based file uploads are one specialised use case. However, most automated web application security scanners are not adapting their attacks when encountering file uploads and are therefore likely to miss vulnerabilities related to file upload functionalities.
While a lot of techniques used for file upload testing are documented throughout the web, the code necessary to automate such attacks is often missing. In other cases, the techniques only apply to very specific use cases. One of the goals of this research was to generalise and automate these attacks. The attack techniques include generic attacks such as Cross Site Scripting (XSS), External Entity Injection (XXE) and PHP/JSP/ASP code injection, but the goal is to execute these attacks customised for the use case of HTTP based file uploads. Additionally, more specific attacks on server side parsers are used as an attack vector, for example Server Side Request Forgery (SSRF) through m3u8 playlist file formats being parsed with LibAv.
File uploads on websites are an underestimated area for security testing. The attack surface on a server that parses files is automatically a lot bigger. While some of the issues that might occur get very high attention (eg. the ImageTragick vulnerability), there are countless memory corruption bugs that get fixed every day in various parses that might also be in use on your webserver. And while your REST XML web service might not be vulnerable to XML External Entity (XXE) injection, it doesn't mean your image parser for JPEG XMP metadata (which is XML) has no XXE issue.
Various techniques are necessary to successfully upload a file, including correlation of file extensions, content types, and content. Moreover, the file content has to pass server-side checks or modifications such as image size requirements or resizing operations. Circumventing processing on the server side, creating content that survives the modification or creating content that results in the desired payload after the modification is another goal of this extension.
While there are already a couple of Burp extensions doing some checks, this extension tries to implements most attacks that seem feasible for file uploads. The extension is testing various attacks and is divided into modules. Each module handles several attacks of the same category.
While the extension has various interesting features in its various modules, one of the main features is:
There are several tutorial videos available for the different topics that will help you get started. The UI of the extension changed a little since the videos were made, but it should be possible to get the basic ideas:
|Author||Tobias 'floyd' Ospelt, modzero AG|
|Last updated||13 September 2018|
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