GHSA-2cf7-hpwf-47h9 n8n-MCP: Incorrect authorization can expose default-scope workflow version backups in multi-tenant HTTP mode

• npm n8n-mcp: < 2.57.4 → fixed in 2.57.4

Summary In multi-tenant HTTP mode (`ENABLE_MULTI_TENANT=true`), an authenticated tenant could, under certain conditions, reach n8n-mcp's local default-scope `workflow_versions` backups instead of being confined to its own tenant scope. This affects n8n-mcp's own local workflow-version storage, not a normal n8n API capability. Impact An authenticated MCP HTTP tenant could read or delete workflow-version backups stored in the default (single-tenant) scope — for example backups left from a prior single-tenant deployment or a migration period. Workflow snapshots may contain sensitive workflow configuration depending on their contents. Single-tenant and stdio deployments are not affected. Affected versions `<= 2.57.3` Patched version `2.57.4` Remediation Upgrade to n8n-mcp `2.57.4` or later. The fix requires a complete tenant context in multi-tenant mode and fails closed for workflow-version access that cannot be attributed to a specific tenant. Workarounds • Restrict network access to the HTTP endpoint (firewall / reverse proxy / VPN) so only trusted callers can reach it. • Run in stdio mode, which has no multi-tenant HTTP surface. • If default-scope backups from a prior single-tenant deployment are not needed, removing them eliminates the exposure. Credit Reported by @DavidCarliez.