npm · @grackle-ai/plugin-core
Grackle: Fail-open authorization in the MCP tool layer lets scoped agents perform cross-task and cross-session mutations (IDOR)
Authorization for scoped (agent) MCP callers is enforced inline, per tool, and is applied inconsistently — several mutating tools silently omit the ancestry/workspace check that their siblings perform. Because the MCP server authenticates all outbound gRPC with the full server API key and the backend gRPC handlers perform no caller-based authorization, the MCP tool layer is the sole authorization boundary. A malicious or prompt-injected scoped agent can therefore perform cross-task and cross-session operations it should not be allowed to (an IDOR / privilege-boundary bypass).
This advisory bundles the audit's Systemic Pattern A findings: F2, F6, F7, F12 (and the duplicate F19).
@grackle-ai/mcp (with @grackle-ai/plugin-core / @grackle-ai/auth) at 0.132.1 and earlier.
mcp-server.ts:111-127 (createGrpcClients) sets Authorization: Bearer ${apiKey} (the full server key) on every outbound gRPC call.updateTask, deleteTask, resumeTask, killAgent, getTask in plugin-core) take only the request message — no AuthContext — and act on whatever ID is passed.assertCallerIsAncestor (task_complete, task_start, session_attach, session_send_input); their destructive siblings do not. New tools that forget the check fail open.Location: packages/mcp/src/tools/task.ts:226 (task_update), :393 (task_delete), :465 (task_resume).
These accept an arbitrary taskId with only a ROOT_TASK_ID special-case and no assertCallerIsAncestor. The central dispatcher hardcodes its workspace gate to name === "task_show", and these tools' Zod schemas have no workspaceId field (so the blanket injection is stripped). They are not in DEFAULT_SCOPED_MCP_TOOLS but are in the shipped ORCHESTRATOR_MCP_TOOLS / ADMIN_MCP_TOOLS presets.
Exploit: a scoped agent under the orchestrator persona learns a sibling/parent/cross-workspace task ID (via task_list/task_search), then task_delete {taskId: <victim>} (permanently destroys another agent's or the human parent's work) or task_update to flip a sibling to complete/failed or rewrite its dependency DAG and budgets.
Location: packages/mcp/src/tools/session.ts:95 (session_resume), :178 (session_kill).
Call client.killAgent / client.resumeAgent directly with no auth context, unlike session_attach/session_send_input. session_kill is in the orchestrator preset. Exploit: cross-session SIGKILL DoS against a sibling agent or the root orchestrator; foreign session resume.
Location: packages/mcp/src/mcp-server.ts:565-600.
The per-task cross-workspace check (task_show block) is gated on authContext.workspaceId being truthy. A task created without a workspace (a supported config) mints a scoped token with pid: "" → workspaceId: undefined, so the check is skipped and the injected workspaceId becomes "", which the backend treats as "all workspaces." Exploit: a malicious agent in a workspaceless session calls task_list (no args) → reads every task in every workspace, then task_show {taskId} cross-workspace (title/description/branch/review-notes). schedule_show (in the default scoped allowlist) resolves by ID with no workspace check. Read-only cross-workspace disclosure.
Location: packages/auth/src/scoped-token.ts:23,142-149.
The consuming check is wired (auth-middleware.ts:90-92), but revokeTask() is never called outside tests — no task-abort/stop flow invokes it — and the backing revokedTasks Map is in-memory only (lost on restart). A compromised agent that exfiltrated its scoped token keeps authenticating for the full 24h TTL regardless of task lifecycle.
CallToolRequest dispatcher (mcp-server.ts) via a per-tool targetTaskIdArg / targetSessionIdArg descriptor so any tool that targets a task/session fails closed unless the caller is an ancestor (or self).assertCallerIsAncestor (or self-or-ancestor) to task_update, task_delete, task_resume, session_kill, session_resume, mirroring task_complete/task_start.workspaceId — treat a scoped non-root caller with no workspace as having access to no workspace; apply the task_show membership check whenever the caller is scoped and not ROOT_TASK_ID; add a per-id membership check to schedule_show.revokeTask() into task-abort/stop flows with SQLite-backed persistence (like channel-grant revocation), or remove the dead API and document the 24h window.task_complete ancestor tests for each mutator.CWE-862 (Missing Authorization), CWE-639 (Authorization Bypass Through User-Controlled Key / IDOR), CWE-613 (Insufficient Session Expiration).
Is your project exposed to this? Stateward checks every dependency on every pull request and flags it only if your code actually reaches it.
Check my repoSources: CISA KEV (public domain), OSV.dev & GitHub Advisory Database (CC-BY-4.0), FIRST EPSS, NVD/CWE (public domain). Served live from the Stateward advisory database.