stigmem-node: RTBF tombstones are mis-attributed and suppress reads tenant-blind (cross-tenant BOLA)

Summary

On a multi-tenant stigmem node, RTBF (right-to-be-forgotten) tombstones were mis-scoped two ways. (1) issue_tombstone defaulted the tenant to "default" instead of the caller's tenant, so tombstones could be written to the wrong tenant. (2) The read-suppression path — _get_tombstone_filter (routes/facts/common.py) and the _tombstone_scope_cache (lifecycle/tombstones.py) — had no tenant_id predicate, so tombstone suppression was applied tenant-blind across fact queries and provenance. Reached via /v1/tombstones and the fact query/provenance read paths.

Impact

Cross-tenant integrity of the RTBF mechanism: a tenant's deletion request could be recorded against the wrong tenant, and tombstone suppression could hide — or fail to hide — facts across tenant boundaries, undermining both data-view correctness and RTBF guarantees.

Affected configurations

This is a cross-tenant break. It is exploitable only on deployments running the opt-in stigmem-plugin-multi-tenant (multiple tenants on one node). A default single-tenant node has only tenant="default" — there is no second tenant to cross — so it is not exploitable on default deployments. The rating is HIGH for the multi-tenant deployments the plugin exists to isolate.

Patches

Fixed in 0.9.0a12 (PR #728): identity.tenant_id is passed from issue_tombstone into create_tombstone (no more "default" fallback); AND tenant_id = ? was added to _get_tombstone_filter and get_tombstone_status; the suppression cache is re-keyed to include tenant; and all four read call sites thread the caller's tenant. A tenant-B tombstone now suppresses only tenant-B facts and is invisible to tenant-A reads.

Workarounds

None other than upgrading to 0.9.0a12. Single-tenant deployments are unaffected.