GHSA-cp3j-m783-3ph5

## Summary

identrail's GitHub App connection-completion endpoint binds a fully client-supplied `installation_id` to the caller's workspace without verifying that the installation belongs to, or was installed by, the workspace that initiated the connect flow. identrail then mints a GitHub App installation access token for the supplied `installation_id` using the app's own JWT, so an authenticated tenant can link any other identrail customer's GitHub App installation into their own workspace and read that victim organization's private repositories.

## Affected code (default-on path, no feature flag)

- Route: `internal/api/router.go:3590` — `POST /v1/workspaces/:workspace_id/projects/:project_id/github/connect/complete`. `installation_id` is read from the JSON body or the attacker-controlled `X-GitHub-Installation-ID` header (`router.go:3582-3588`). - Service: `internal/api/github_connect.go:781` `CompleteGitHubConnection`. The `state` token IS rigorously bound to the caller's scope (`github_connect.go:818`: `if stateRecord.TenantID != scope.TenantID || stateRecord.WorkspaceID != project.WorkspaceID || stateRecord.ProjectID != project.ProjectID { ... }`), but the only check on `installation_id` is `request.InstallationID <= 0` (`:794`). The raw client value is persisted as the workspace's connection (`:840`). - Cross-tenant read primitive: `internal/connectors/github/repositories.go:39` `ListInstallationRepositories` → `internal/connectors/github/app.go:170` mints a token via `POST /app/installations/{installationId}/access_tokens` signed with the App JWT, succeeding for any installation where identrail's app is installed.

The feature-flagged V2 path `CompleteGitHubConnector` (`github_connect.go:447`, default off) shares the gap and is additionally weaker (matches pending connector by `state` value alone with no caller-scope re-check); a single fix should cover both.

## Intent proof

The code binds `state` to `{TenantID, WorkspaceID, ProjectID}` and re-verifies it at completion (`:818`), demonstrating it understands binding is required. The asymmetry — `state` bound, `installation_id` unbound — is the missed check.

## Exploitation

1. Attacker is any authenticated identrail tenant; they call `StartGitHubConnection` for their own workspace and receive a `state`. 2. Attacker calls the completion route with `{state: <their state>, installation_id: V}` where V is a victim org's identrail GitHub App installation id (installation ids are not secret — they appear in post-install redirect URLs, webhook payloads, the org's GitHub App settings, and are enumerable integers). 3. `CompleteGitHubConnection` accepts (state matches attacker scope), `ListInstallationRepositories(V)` mints a token for V and lists the victim org's private repos, and the connection is persisted under the attacker's workspace. 4. Attacker now reads the victim org's private repository inventory and can drive posture scans/repo reads via their own workspace.

Impact: cross-tenant disclosure of another customer organization's private GitHub repositories and metadata.

## Remediation

Bind `installation_id` with the same rigor as `state`: capture it from GitHub's signed post-install redirect (`setup_url`/`callback_url`) and pin it to the pending state at start time, and/or after minting verify the installation's `account` matches the org the initiating workspace is authorized for.