Semaphore UI is a web interface for managing DevOps tools. Prior to 2.18.19 and from 2.19.0-alpha3 until 2.19.5-beta5, ProjectMiddleware and GetProjectOrGlobalRoleBySlug allow a project manager to use POST /api/project/{id}/roles to create a custom manager role with permission bitmask 15, overriding the built-in manager permissions and granting CanUpdateProject and CanManageProjectUsers owner capabilities. This issue is fixed in versions 2.18.19 and 2.19.5-beta5.

Affected: Go: github.com/semaphoreui/semaphore

## 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 projec…