Remote code execution in dependabot-core branch names when cloning
### Impact
Remote code execution vulnerability in `dependabot-common` and `dependabot-go_modules` when a source branch name contains malicious injectable bash code.
For example, if Dependabot is configured to use the following source branch name: `"/$({curl,127.0.0.1})"`, Dependabot will make a HTTP request to the following URL: 127.0.0.1 when cloning the source repository.
When Dependabot is configured to clone the source repository during an update, Dependabot runs a shell command to git clone the repository:
```bash
git clone --no-tags --no-recurse-submodules --depth=1 --branch=<BRANCH> --single-branch <GITHUB_REPO_URL> repo/contents/path
```
Dependabot will always clone the source repository for `go_modules` during the file fetching step and can be configured to clone the repository for other package managers using the `FileFetcher` class from `dependabot-common`.
```ruby
source = Dependabot::Source.new(
provider: "github",
repo: "repo/name",
directory: "/",
branch: "/$({curl,127.0.0.1})",
)
repo_contents_path = "./file/path"
fetcher = Dependabot::FileFetchers.for_package_manager("bundler").
new(source: source, credentials: [],
repo_contents_path: repo_contents_path)
fetcher.clone_repo_contents
```
### Patches
The fix was applied to version `0.125.1`:
https://github.com/dependabot/dependabot-core/pull/2727
### Workarounds
Escape the branch name prior to passing it to the `Dependabot::Source` class.
For example using `shellwords`:
```ruby
require "shellwords"
branch = Shellwords.escape("/$({curl,127.0.0.1})")
source = Dependabot::Source.new(
provider: "github",
repo: "repo/name",
directory: "/",
branch: branch,
)
```