Securely using pull_request_target

This guide helps you assess whether your workflow should use the pull_request_target event and understand the security risks involved. It also explains the protection GitHub applies to actions/checkout v7 and later to reduce these risks by default, and when to opt out of that protection if necessary.

Read pull_request_target before you check out pull request code from one of these workflows, or before you set the allow-unsafe-pr-checkout input on actions/checkout.

The risks of the pull_request_target event

Workflows triggered by pull_request_target run with elevated trust: the job receives the base repository's GITHUB_TOKEN, access to repository and organization secrets, and write access to the default-branch cache. This is the same trust given to events like push that only collaborators can trigger, and it is what makes pull_request_target useful for automation that responds to pull requests from forks, such as labeling, triage, or for posting authenticated status checks.

To understand why this is safe by default, and how that safety is commonly broken, review pull_request_target against pull_request.

The pull_request event (along with pull_request_review and pull_request_review_comment) is unusual: it runs the workflow file from the merge commit of the pull request. For a pull request opened from a fork, that commit is controlled by someone without write access to the base repository. To run untrusted workflow code safely, GitHub restricts these events to a read-only GITHUB_TOKEN, withholds access to other secrets, and applies fork approval policies to prevent compute abuse. For more information, see Eventos que desencadenan flujos de trabajo. By default, actions/checkout in a pull_request workflow also checks out the pull request's merge commit, so the code checked out and the workflow that runs are consistent.

pull_request_target makes one critical and subtle change: the workflow, and any subsequent actions/checkout call that does not specify a ref, is taken from the base repository's default branch, not from the pull request. Because only trusted code from the default branch runs, it is safe to grant secrets and a read/write token. No code from the fork is executed by default.

You introduce risk when a workflow author overrides this default to run the fork's code. Developers frequently choose pull_request_target because they want to run a fork's pull request through CI and have access to secrets, for example to run tests that need a private registry. To do this, they point actions/checkout at the pull request head instead of the default branch, which is insecure:

# INSECURE. Provided as an example only.
on:
  pull_request_target:

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v6
        with:
          ref: ${{ github.event.pull_request.head.sha }}
      - name: Test
        run: make test

The checkout step alone does not execute untrusted code. The workflow file itself still comes from the default branch. The vulnerability is completed by the next step that runs code checked out into the current working directory. Here, make test executes a Makefile taken from the pull request head. An attacker only needs to open a pull request from a fork whose Makefile (or build script, test command, dependency, or configuration file) contains malicious commands. Those commands then run with the base repository's secrets and token.

This pattern is known as a "pwn request" and has been the root cause of multiple supply-chain compromises. For more information, see Preventing pwn requests from the GitHub Security Lab. Common vulnerable shapes include:

• Checking out a pull request's head or merge commit in actions/checkout (ref: ${{ github.event.pull_request.head.sha }}, ref: refs/pull/${{ github.event.pull_request.number }}/merge) and then building, testing, or otherwise executing the result.
• Setting repository: to the fork (repository: ${{ github.event.pull_request.head.repo.full_name }}) to pull the fork's branch directly.
• Fetching the pull request code outside of actions/checkout (for example with git fetch, gh pr checkout, or by downloading an artifact from a fork's pull_request run) and then running it.

Pwn requests are also not unique to pull_request_target. Any event that runs with secrets can introduce a pwn request if it checks out or downloads and executes untrusted code. For example, an issue_comment or workflow_run workflow that fetches and runs a fork's pull request code is vulnerable in the same way. A workflow_run workflow should treat artifacts uploaded by other workflows as untrusted data, since their contents can come from a fork.

Deciding whether to use pull_request_target

Some workflows need to check out fork pull request code with elevated trust, and this is why pull_request_target was created in the first place. For example, generating coverage reports that require a private artifact registry or producing and running authenticated checks against the changes introduced from the pull request. Consider the questions below before using pull_request_target or opting into the allow-unsafe-pr-checkout flag in actions/checkout.

• Can you use pull_request instead? pull_request triggers on the same events as pull_request_target and runs the workflow code from the pull_request merge branch. It does this safely on pull requests from forks with the protections detailed above. If additional secret access is not needed, use pull_request. More complex workflows can be restructured to separate potentially dangerous handling of pull request code from accessing secrets. For more information, see Preventing pwn requests from the GitHub Security Lab.

• Is the checked-out code ever executed? This is the flaw that introduces pwn request vulnerabilities. It is most commonly introduced with actions/checkout by checking out a pull request head into the working directory and then running it. Unless the path input is set, actions/checkout writes the code into the $GITHUB_WORKSPACE directory, which is typically the working directory where subsequent commands run. Execution is not limited to your own steps: build and test commands such as npm install and npm run build, as well as configuration files and dependencies the code brings with it, can all run attacker-controlled code. Execution does not require an obvious build step. You must ensure the checked-out code is only ever inspected as data and never executed before using a pull_request_target event.

Hardening a pull_request_target workflow

If you have confirmed you need pull_request_target, apply these controls to limit the impact of this high-risk event. These apply whether or not your workflow checks out pull request code.

• Restrict secrets. Confirm that the permissions set on the GITHUB_TOKEN have the least privileges and that only the necessary repository and organization secrets are used for the workflow. For more information, see Uso de GITHUB_TOKEN para la autenticación en flujos de trabajo.

• Understand the impact to caching. Outside of the GITHUB_TOKEN and configured secrets, workflows that run on pull_request_target also have write access to the cache shared with other workflows on the default branch. Malicious changes to this cache from pull_request_target events could impact the execution of other, unrelated, workflows.

• Ensure the underlying compute is isolated and ephemeral. If self-hosted runners are used, you must confirm that the runner environment is properly restricted from internal resources and is not reused across GitHub Actions runs. For more information, see Referencia de uso seguro.

• Gate runs behind approval. pull_request_target workflows can be gated behind a required label that only users with write access can add. This is detailed in the GitHub Security Lab guidance on preventing pwn requests.

• Enforce GitHub Actions security best practices. In addition to the specific risks of pwn requests, other common vulnerabilities, such as command injection, can exist and impact the code executed in this privileged event. For more information, see Keeping your GitHub Actions and workflows secure: Untrusted input from the GitHub Security Lab. To identify and proactively protect against common GitHub Actions vulnerabilities, enable CodeQL for GitHub Actions. For more information, see Establecimiento de la configuración predeterminada para el examen del código.

Opting out of built-in protections

If you have worked through the questions above and confirmed your workflow requires pull_request_target and uses it safely, you can opt out of the actions/checkout protection. Setting allow-unsafe-pr-checkout: true as an actions/checkout input allows checking out pull request head refs from forks. Only do this after confirming the checked-out code is never executed. The input is intentionally named to be easy to spot in code review and static analysis.

This protection only covers fork pull request refs. Checking out other untrusted code, such as an unrelated third-party repository, fetching code with git fetch or gh pr checkout, or running a downloaded artifact, is not covered by the actions/checkout checks.

Restricting the use of pull_request_target

Repository, organization, and enterprise administrators can use Workflow execution protections to control which events and actors can trigger workflows. If a repository has no legitimate use for pull_request_target, restricting it removes the risk regardless of how individual workflows are written.