Assembly security

Question

I'm currently offering an assembly compile service for some people. They can enter their assembly code in an online editor and compile it. When then compile it, the code is sent to my server with an ajax request, gets compiled and the output of the program is returned.

However, I'm wondering what I can do to prevent any serious damage to the server. I'm quite new to assembly myself so what is possible when they run their script on my server? Can they delete or move files? Is there any way to prevent these security issues?

Thank you in advance!

Answer 1

Have a look at http://sourceforge.net/projects/libsandbox/. It is designed for doing exactly what you want on a linux server:

This project provides API's in C/C++/Python for testing and profiling simple (single process) programs in a restricted environment, or sandbox. Runtime behaviours of binary executable programs can be captured and blocked according to configurable / programmable policies.

The sandbox libraries were originally designed and utilized as the core security module of a full-fledged online judge system for ACM/ICPC training. They have since then evolved into a general-purpose tool for binary program testing, profiling, and security restriction. The sandbox libraries are currently maintained by the OpenJudge Alliance (http://openjudge.net/) as a standalone, open-source project to facilitate various assignment grading solutions for IT/CS education.

Answer 2

If this is a tutorial service, so the clients just need to test miscellaneous assembly code and do not need to perform operations outside of their program (such as reading or modifying the file system), then another option is to permit only a selected subset of instructions. In particular, do not allow any instructions that can make system calls, and allow only limited control-transfer instructions (e.g., no returns, branches only to labels defined within the user’s code, and so on). You might also provide some limited ways to return output, such as a library call that prints whatever value is in a particular register. Do not allow data declarations in the text (code) section, since arbitrary machine code could be entered as numerical data definitions.

Although I wrote “another option,” this should be in addition to the others that other respondents have suggested, such as sandboxing.

This method is error prone and, if used, should be carefully and thoroughly designed. For example, some assemblers permit multiple instructions on one line. So merely ensuring that the text in the first instruction field of a line was acceptable would miss the remaining instructions on the line.

Answer 3

Compiling and running someone else's arbitrary code on your server is exactly that, arbitrary code execution. Arbitrary code execution is the holy grail of every malicious hacker's quest. Someone could probably use this question to find your service and exploit it this second. Stop running the service immediately. If you wish to continue running this service, you should compile and run the program within a sandbox. However, until this is implemented, you should suspend the service.

You should run the code in a virtual machine sandbox because if the code is malicious, the sandbox will prevent the code from damaging your actual OS. Some Virtual Machines include VirtualBox and Xen. You could also perform some sort of signature detection on the code to search for known malicious functionality, though any form of signature detection can be beaten.

This is a link to VirtualBox's homepage: https://www.virtualbox.org/

This is a link to Xen: http://xen.org/