The [`tj-actions/verify-changed-files`](https://github.com/tj-actions/verify-changed-files) action allows for command injection in changed filenames, allowing an attacker to execute arbitrary code and potentially leak secrets. The [`verify-changed-files`](https://github.com/tj-actions/verify-changed-files) workflow returns the list of files changed within a workflow execution. This could potentially allow filenames that contain special characters such as `;` 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`.

This has been patched in versions [17](https://github.com/tj-actions/verify-changed-files/releases/tag/v17) and [17.0.0](https://github.com/tj-actions/verify-changed-files/releases/tag/v17.0.0) by enabling `safe_output` by default and returning filename paths escaping special characters for bash environments.

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

### Summary The [`tj-actions/verify-changed-files`](https://github.com/tj-actions/verify-changed-files) action allows for command injection in changed filenames, allowing an attacker to execute arbitrary code and potentially leak secrets.

### Details The [`verify-changed-files`](https://github.com/tj-actions/verify-changed-files) workflow returns the list of files changed within a workflow execution.

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 the repository with a new file injecting a command. For example `$(whoami).txt` would be 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 tracked and untracked files` step.

```yaml - name: List all changed files tracked and untracked files run: | echo "Changed files: ${{ steps.verify-changed-files.outputs.changed_files }}" ```

Example output:…