Keystone has an unintended `isFilterable` bypass that can be used as an oracle to match hidden fields

Summary

{field}.isFilterable access control can be bypassed in update and delete mutations by adding additional unique filters. These filters can be used as an oracle to probe the existence or value of otherwise unreadable fields.

Specifically, when a mutation includes a where clause with multiple unique filters (e.g. id and email), Keystone will attempt to match records even if filtering by the latter fields would normally be rejected by field.isFilterable or list.defaultIsFilterable. This can allow malicious actors to infer the presence of a particular field value when a filter is successful in returning a result.

Impact

This affects any project relying on the default or dynamic isFilterable behaviour (at the list or field level) to prevent external users from using the filtering of fields as a discovery mechanism. While this access control is respected during findMany operations, it was not completely enforced during update and delete mutations when accepting more than one unique where values in filters.

This has no impact on projects using isFilterable: false or defaultIsFilterable: false for sensitive fields, or if you have otherwise omitted filtering by these fields from your GraphQL schema. (See workarounds)

Patches

This issue has been patched in @keystone-6/core version 6.5.0.

Workarounds

To mitigate this issue in older versions where patching is not a viable pathway.

• Set isFilterable: false statically for relevant fields to prevent filtering by them earlier in the access control pipeline (that is, don't use functions)
• Set {field}.graphql.omit.read: true for relevant fields, which implicitly removes filtering by these fields your GraphQL schema
• Deny update and delete operations for the relevant lists completely (e.g list({ access: { operation: { update: false, delete: false } }, ... }))