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:

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.

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:

require "shellwords"
branch = Shellwords.escape("/$({curl,127.0.0.1})")
source = Dependabot::Source.new(
  provider: "github",
  repo: "repo/name",
  directory: "/",
  branch: branch,
)