A moderate security vulnerability has been identified in the GitHub Actions runner that can allow environment variable and path injection in workflows that log untrusted data to STDOUT. This can result in environment variables being introduced or modified without the intention of the workflow author.

To allow us to address this issue and maintain the ability for you to dynamically set environment variables we have introduced a new set of files to manage environment and path updates in workflows.

Patching your actions and workflows

If you are using self-hosted runners make sure they are updated to version 2.273.1 or greater.

Action authors who are using the toolkit should update the @actions/core package to v1.2.6 or greater to get the updated addPath and exportVariable functions.

Action and workflow authors who are setting environment variables via STDOUT should update any usage of the set-env and add-path workflow commands to use the new environment files.

If you need to log untrusted information such as issue titles, bodies, or commit messages to STDOUT we recommend that you disable command processing prior to doing that.

As an example in bash you could do the following:

    name: example
    runs-on: ubuntu-latest
    - name: log untrusted output
      run: |

        # disable command workflow processing
        echo "::stop-commands::`echo -n ${{ github.token }} | sha256sum | head -c 64`"

        # log untrusted output
        echo "untrusted output"

        # enable workflow command processing
        echo "::`echo -n ${{ github.token }} | sha256sum | head -c 64`::"

In a JavaScript Action:

import {v4 as uuidv4} from 'uuid'

// disable workflow commands
const token = uuidv4()

// log untrusted output
console.log("untrusted output")

// enable workflow commands

For other languages you need to generate a suitably random token that changes with each run.

See Stopping and starting workflow commands to learn more.

Starting today runner version 2.273.5 will begin to warn you if you use the add-path or set-env commands. We are monitoring telemetry for the usage of these commands and plan to fully disable them in the future.

Learn more about CVE-2020-15228

@actions/core npm package

Learn more about the new environment files

For questions please visit the GitHub Actions community forum