While I was doing a pentest last month, I discovered an attack I didn't previously know, and I thought I'd share it. This may be a Christopher Columbus moment - discovering something that millions of people already knew about - but I found it pretty cool so now you get to hear about it!
One of the first things I do when I'm looking at a Web app - and it's okay to make a lot of noise - is run the http-enum.nse Nmap script. This script uses the http-fingerprints.lua file to find any common folders on a system (basically brute-force browsing). I'm used to seeing admin folders, tmp folders, and all kinds of other interesting stuff, but one folder in particular caught my eye this time - /.git.
Now, I'll admit that I'm a bit of an idiot when it comes to git. I use it from time to time, but not in any meaningful way. So, I had to hit up my friend @mogigoma. He was on his cellphone, but managed to get me enough info to make this attack work.
First, I tried to use git clone to download the source. That failed, and I didn't understand why, so I gave up that avenue right away.
Next, I wanted to download the /.git folder. Since directory listings were turned on, this was extremely easy:
$ mkdir git-test $ cd git-test $ wget --mirror --include-directories=/.git http://www.target.com/.git
That'll take some time, depending on the size of the repository. When it's all done, go into the folder that wget created and use git --reset:
$ cd www.site.com $ git reset --hard HEAD is now at [...]
Then look around - you have their entire codebase!
$ ls db doc robots.txt scripts test
Browse this for interesting scripts (like test scripts?), passwords, configuration details, deployment, addresses, and more! You just turned your blackbox pentest into a whitebox one, and maybe you got some passwords in the deal! You can also use "git log" to get commit messages, "git remote" to get a list of interesting servers, "git branch -a" to get a list of branches, etc.
Why does this happen?
When you clone a git repository, it creates a folder for git's metadata - .git - in the folder where you check it out. This is what lets you do a simple "git pull" to get new versions of your files, and can make deployment/upgrades a breeze. In fact, I intentionally leave .git folders in some of my sites - like my hackerspace, SkullSpace. You can find this exact code on github, so there's no privacy issue; this only applies to commercial sites where the source isn't available, or where more than just the code is bring stored in source control.
There are a few ways to prevent this:
- Remove the .git folder after you check it out
- Use a .htaccess file (or apache configuration file) to block access to .git
- Keep the .git folder one level up - in a folder that's not available to the Web server
- Use a framework - like Rails or .NET - where you don't give users access to the filesystem
There may be other ways as well, use what makes sense in your environment!
Finding this in an automated way
A friend of mine - Alex Weber - wrote an Nmap script (his first ever!) to detect this vulnerability and print some useful information about the git repository! This script will run by default when you run nmap -A, or you can specifically request it by running nmap --script=http-git <target>. You can quickly scan an entire network by using a command like:
nmap -sS -PS80,81,443,8080,8081 -p80,81,443,8080,8081 --script=http-git <target>
The output for an affected host will look something like:
PORT STATE SERVICE 80/tcp open http | http-git: | Potential Git repository found at 18.104.22.168:80/.git/ (found 5 of 6 expected files) | Repository description: Unnamed repository; edit this file 'description' to name the... | Remote: https://github.com/skullspace/skullspace.ca.git |_ -> Source might be at https://github.com/skullspace/skullspace.ca
And that's all there is to it! Have fun, and let me know if you have any interesting results so I can post a followup!