Delimiter injection vulnerability in @actions/core exportVariable

Vulnerability Description

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`.

References

• https://github.com/actions/toolkit/security/advisories/GHSA-7r3h-m5j6-3q42
• https://github.com/actions/toolkit/commit/4beda9cbc00ba6eefe387a937c21087ccb8ee9df