tj-actions/changed-files is a Github action to retrieve all files and directories. Prior to 41.0.0, the `tj-actions/changed-files` workflow allows for command injection in changed filenames, allowing an attacker to execute arbitrary code and potentially leak secrets. This issue may lead to arbitrary command execution in the GitHub Runner. This vulnerability has been addressed in version 41.0.0. Users are advised to upgrade.

Affected: GitHub Actions: tj-actions/changed-files

### Summary The `tj-actions/changed-files` workflow allows for command injection in changed filenames, allowing an attacker to execute arbitrary code and potentially leak secrets.

### Details The [`changed-files`](https://github.com/tj-actions/changed-files) action returns a list of files changed in a commit or pull request which provides an `escape_json` input [enabled by default](https://github.com/tj-actions/changed-files/blob/94549999469dbfa032becf298d95c87a14c34394/action.yml#L136), only escapes `"` for JSON values.

This could potentially allow filenames that contain special characters such as `;` and \` (backtick) which can be used by an attacker to take over the [GitHub Runner](https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners) if the output value is used in a raw fashion (thus being directly replaced before execution) inside a `run` block. By running custom commands an attacker may be able to steal **secrets** such as `GITHUB_TOKEN` if triggered on other events than `pull_request`. For example on `push`.

#### Proof of Concept

1. Submit a pull request to a repository with a new file injecting a command. For example `$(whoami).txt` which is a valid filename. 2. Upon approval of the workflow (triggered by the pull request), the action will get executed and the malicious pull request filename will flow into the `List all changed files` step below.

```yaml - name: List all changed files run: | for file…