mcp-memory-service: OAuth read-only clients can write and delete memories through MCP tools/call
Date: 2026-06
Affected: pip/mcp-memory-service
Attack vector: auth-bypass
Category: vulnerability-disclosure
Severity: High
CVE: CVE-2026-49291
CWE: CWE-862
CVSS: 8.1 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H)

## Summary The HTTP MCP JSON-RPC endpoint at `/mcp` requires only OAuth `read` scope for all requests, then dispatches `tools/call` directly to handlers that include mutating tools. A read-only OAuth client can call `store_memory` and `delete_memory` through MCP even though the corresponding REST endpoints require `write` scope. ## Technical Details `src/mcp_memory_service/web/api/mcp.py` declares `mcp_endpoint` with `user: AuthenticationResult = Depends(require_read_access)`. For `tools/call`, it extracts the requested tool name and arguments, then calls `handle_tool_call(storage, tool_name, arguments)` without passing the authenticated user or checking a per-tool required scope. The MCP tool registry includes both read tools and write tools. In the same handler file, `store_memory` creates a `Memory` object and calls `storage.store(...)`, while `delete_memory` calls `storage.delete(content_hash)`. These operations are reachable with only the `read` scope. The REST endpoint demonstrates the intended boundary: `POST /api/memories` uses `Depends(require_write_access)` and rejects a read-only token with 403 `insufficient_scope`. ## Reproduction 1. Enable OAuth and disable anonymous access. 2. Generate a valid OAuth JWT with only `scope: read`. 3. Confirm the REST write endpoint rejects it: ```http POST /api/memories Authorization: Bearer <read-only-token> Content-Type: application/json {"content":"rest denied control"} ``` Expected and observed: HTTP 403 with `Require


Mitigations:

Architectural layers (MAESTRO):