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Forestall

GH_COLLABORATOR

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Summary
Forestall ACL Alias GH_COLLABORATOR
Edge Type Relationship
Affected Object Types GitHub Repositories
Exploitation Certainty N/A (structural)
GitHub Role / Permission Any direct repository permission (pull / triage / push / maintain / admin)

Description

GH_COLLABORATOR is a structural relationship recording that a user has been granted access directly on a repository — as a collaborator on the repository itself, not through a team. The permission level is stored on the edge as the Permission property: pull, triage, push, maintain, or admin.

Only direct grants are modelled (collected with affiliation=direct). Access a user inherits through team membership is represented by GH_IN_TEAM → GH_HAS_ACCESS instead, so the two paths stay distinct.

This edge captures all direct user access regardless of level. The privileged subset is derived into separate attack-path edges:

  • A direct collaborator with admin also gets GH_ADMIN.
  • A direct collaborator with push/maintain on an unprotected default branch also gets GH_PUSH_TO_DEFAULT.

Direct collaborator grants are worth attention because they bypass team-based access governance: they are easy to add ad hoc and easy to forget, and outside collaborators frequently appear here.

Identification

GitHub Web Interface

  1. Open the repository → Settings → Collaborators and teams.
  2. The People section lists every user with direct access and their role (Read / Triage / Write / Maintain / Admin).

Exploitation

Not applicable — this is a structural relationship, not a traversable attack path. The security-relevant capabilities a direct collaborator holds are exploited through the privileged edges built on top of it (GH_ADMIN, GH_PUSH_TO_DEFAULT).

Mitigation

  1. Prefer team-based access over direct collaborators. Managing access through teams keeps grants reviewable and consistent; direct grants drift out of governance.

  2. Audit direct collaborators regularly, especially outside collaborators and anyone holding write or above. Remove access that is no longer needed.

  3. Grant the least sufficient permission. Use read/triage unless the user must push, and reserve admin for genuine repository administrators.

Detection

Event Description
repo.add_member A user was added as a collaborator on the repository
repo.remove_member A collaborator was removed from the repository
repo.update_member A collaborator’s permission level was changed

Alert on direct grants of write/admin, on access granted to outside collaborators, and on permission escalations performed outside an approved change process.

References

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