SurrealDB: Field-level SELECT permissions bypassed via indexed COUNT fast paths

A record user could learn the value of a hidden field by counting how many records match a guess.

When DEFINE FIELD ... PERMISSIONS FOR select WHERE ... hides a field's contents from a caller, and that field is indexed, running SELECT count() FROM t WHERE hidden_field = "guess" GROUP ALL returned a count greater than zero whenever a record actually had that value — even though the caller was never allowed to read the field directly. The query planner used an indexed-COUNT shortcut (Index::Count, IndexCountScan, or the legacy Iterate Index Count / Iterate Index Keys paths) that counts matching index entries and skips the permission check that would normally hide the value. The same query with WITH NOINDEX correctly returned [], confirming the gap.

By repeating the count query with different guesses, an attacker can confirm or recover the contents of any restricted field they could not read through a normal SELECT.

Impact

What an attacker can do:

• Confirm or recover values of a field protected by field-level SELECT permissions on any table they hold table-level SELECT on, provided the field is indexed.
• Repeat the query with different guesses to read restricted field contents one value at a time.

What it can't do:

• Read fields that are not indexed (the shortcut only fires when an index covers the predicate column).
• Cross table, database or namespace isolation boundaries.
• Modify data, escalate privileges, or affect availability.

Patches

The legacy planner (surrealdb/core/src/idx/planner/tree.rs) and the streaming planner (surrealdb/core/src/exec/planner/select/mod.rs) now both refuse the indexed fast path when the WHERE / ORDER tree references a field governed by a non-Full SELECT permission:

• resolve_indexes skips any B-tree / unique index whose columns are governed by such a permission.
• A new cond_touches_restricted_field flag is propagated; eval_count refuses a dedicated Index::Count when set.
• The streaming planner adds cond_touches_restricted_select_field, a RestrictedIdiomChecker visitor that matches each idiom against the table's field-permission prefixes (loaded via the plan-time txn), and gates IndexCountScan emission on it.
• The fast paths are preserved for root / owner sessions via should_check_perms_for_view.

Versions 3.1.0 and later are not affected.

Workarounds

Users unable to patch are advised to consider the following workarounds:

• Avoid DEFINE INDEX on fields whose values are protected by field-level SELECT permissions. The class of attack is specific to the indexed fast paths.
• Restrict the ability of record users to issue arbitrary SELECT count() … GROUP ALL queries against tables containing field-protected columns.
• Use namespace / database isolation as the primary boundary where feasible.