Details on a vulnerability impacting GitHub Actions were made public this week by Google, following a 104-day disclosure deadline.
The bug was identified by security researcher Felix Wilhelm of Google Project Zero, who reported it to GitHub on July 21. As per Google’s policy, information on the flaw was meant to be released after 90 days, but GitHub requested a 14-day grace period.
Tracked as CVE-2020-15228, the vulnerability is related to the use of the set-env and add-path workflow commands, which are set to be disabled. GitHub has assigned the issue a moderate severity rating, but Google Project Zero says it’s high severity.
The set-env command supported by the Github action runner enables the user to define arbitrary environment variables, and the security researcher discovered that the feature is highly susceptible to injection attacks.
“As the runner process parses every line printed to STDOUT looking for workflow commands, every Github action that prints untrusted content as part of its execution is vulnerable. In most cases, the ability to set arbitrary environment variables results in remote code execution as soon as another workflow is executed,” Wilhelm notes.
The issue, GitHub confirms, is that paths and environment variables can be injected into workflows that log untrusted data to stdout, all without the intention of the workflow author.
In an October 1 post, the Microsoft-owned platform revealed that the @actions/core npm module should be updated to version 1.2.6, which updates the addPath and exportVariable functions.
GitHub introduced a new set of files meant for the management of environment and path updates in workflows, to ensure that users can continue to dynamically set environment variables.
“The runner will release an update that disables the set-env and add-path workflow commands in the near future. For now, users should upgrade to @actions/core v1.2.6 or later, and replace any instance of the set-env or add-path commands in their workflows with the new Environment File Syntax,” GitHub explains.
Runner version 2.273.5 is already warning on the use of the add-path or set-env commands, and the plan is to fully disable them, GitHub said. Users are advised to upgrade as soon as possible, as no workarounds have been identified.