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Confidential notes are visible to non-project members/unauthenticated users via project's RSS feed

HackerOne report #1130704 by jimeno on 2021-03-19, assigned to GitLab Team:

Report | Attachments | How To Reproduce

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Steps to reproduce

Victim needs to create a project and post a confidential note to it.

  1. As your victim, create a public project.

    create_public_project.png

  2. Create a MR on your project.

    create_test_mr.png

  3. Find the MR object ID via the GraphQL API explorer. Replace my fullPath with yours.

    {  
  project(fullPath: "naaytesting2/h1testpublicproject") {  
    mergeRequest(iid: "1") {  
      id  
    }  
  }  
}

    find_mr_id.png

  4. Add a confidential note the MR as your victim user. We use the GraphQL API explorer again for this. Replace the noteableId with the one you obtained in previous step.

    mutation xyz {  
  createNote(input: {noteableId: "gid://gitlab/MergeRequest/92779506", body: "confidential note", confidential: true}) {  
    errors  
    clientMutationId  
  }  
}

    create_confidential_note.png

  5. Confirm the confidential note was added to the MR by browsing to your MR and refreshing the page.

    verify_confidential_note_was_created.png

  6. As your attacker, who is not a member of the project, visit the MR and confirm you can't view the confidential note.

    attacker_does_not_see_confidential_note_via_ui.png

  7. As your attacker, browse to the RSS feed of the affected project https://gitlab.com/victimuser/projectname.atom and confirm you can read the confidential note created by victim.

    rss_feed_discloses_confidential_note.png

  8. Confirm you can view the confidential note as an unauthenticated user via a simple curl call to the RSS feed of the affected project.

    $ curl -s https://gitlab.com/naaytesting2/h1testpublicproject.atom | grep confi  
<p data-sourcepos="1:1-1:17" dir="auto">confidential note</p>
Impact

Confidential notes are visible to non-project members via project's RSS feed while the UI restricts the access to them.

Examples

Example project: https://gitlab.com/naaytesting2/h1testpublicproject.

Visit the MR at https://gitlab.com/naaytesting2/h1testpublicproject/-/merge_requests/1 and confirm you can't see the confidential note.

Visit https://gitlab.com/naaytesting2/h1testpublicproject.atom and confirm you can read the confidential note (<p data-sourcepos="1:1-1:17" dir="auto">confidential note</p>).

Please, find the example project exported and attached as a ZIP file. 2021-03-19_14-32-420_naaytesting2_h1testpublicproje_export.tar.gz

What is the current bug behavior?

Confidential notes are available to non-project members via RSS feed of the project.

What is the expected correct behavior?

Confidential notes aren't visible to non-project members via RSS feed of the project.

Relevant logs and/or screenshots

N/A

Output of checks

This bug happens on GitLab.com

Results of GitLab environment info

N/A

Impact

Confidential notes are visible to non-project members or unauthenticated users via project's RSS feed while the UI restricts the access to them.

Attachments

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How To Reproduce

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