The GitHub Actions ToolKit provides a set of packages to make creating actions easier. The `core.exportVariable` function uses a well known delimiter that attackers can use to break out of that specific variable and assign values to other arbitrary variables. Workflows that write untrusted values to the `GITHUB_ENV` file may cause the path or other environment variables to be modified without the intention of the workflow or action author. Users should upgrade to `@actions/core v1.9.1`. If you are unable to upgrade the `@actions/core` package, you can modify your action to ensure that any user input does not contain the delimiter `_GitHubActionsFileCommandDelimeter_` before calling `core.exportVariable`.

Affected: npm: @actions/core

## Impact

The `core.exportVariable` function uses a well known delimiter that attackers can use to break out of that specific variable and assign values to other arbitrary variables. Workflows that write untrusted values to the `GITHUB_ENV` file may cause the path or other environment variables to be modified without the intention of the workflow or action author.

## Patches

Users should upgrade to `@actions/core v1.9.1`.

## Workarounds

If you are unable to upgrade the `@actions/core` package, you can modify your action to ensure that any user input does not contain the delimiter `_GitHubActionsFileCommandDelimeter_` before calling `core.exportVariable`.

## References

[More information about setting-an-environment-variable in workflows](https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#setting-an-environment-variable)

If you have any questions or comments about this advisory: * Open an issue in [`actions/toolkit`](https://github.com/actions/toolkit/issues)