SurrealDB: Writes in a PERMISSIONS clause bypass table permissions

A PERMISSIONS ... WHERE clause is evaluated with permission enforcement disabled, so it can't recurse into its own checks. But the clause could also contain data-modifying statements, and these ran with enforcement still off — so evaluating a permission check could write to tables the caller cannot write.

For example:

DEFINE TABLE post PERMISSIONS FOR update
    WHERE (CREATE log SET at = time::now()) OR true;

Any user allowed to update a post now also creates a log record, even with no permission on log. The clause is evaluated once per matched record, so one statement can cause several writes.

Impact

Only databases with a PERMISSIONS clause that contains a write are affected; FULL, NONE, and read-only clauses are not.

What an attacker can do:

• With permission to perform the guarded operation (a low-privileged or record user is enough), write to tables in their own database that their permissions would otherwise forbid, by triggering an operation the clause guards.
• Cause several writes from a single statement — the clause is evaluated once per matched record.
• Trigger unintended events, cascades, or data corruption on those tables.

What it can't do:

• Escape the caller's own namespace and database — a permission clause cannot switch namespace or database.
• Perform root- or namespace-level actions such as creating users; the caller's role still applies.
• Read hidden data — this is an integrity issue, not disclosure.

Patches

Permission clauses must now be read-only: defining or importing one that contains a write is rejected, and any write attempted while a clause is evaluated is blocked at runtime, including writes reached through a called function. Read-only clauses are unaffected.

• Versions 3.2.0 and later are not affected by this issue.

Workarounds

Users unable to patch should consider the following workarounds:

• Review your PERMISSIONS clauses and remove any containing CREATE, UPDATE, DELETE, RELATE, INSERT, or UPSERT.
• Limit who can define schema and vet imported data — such a clause must be defined before it can be triggered.

Resources

• DEFINE TABLE … PERMISSIONS
• DEFINE FIELD
• fix(core): reject writes in PERMISSIONS clauses and block writes during permission evaluation (included in SurrealDB 3.2.0)

Acknowledgements

Thank you to sondt99 for reporting this issue.