CVE-2026-81318: CWE-863 Incorrect Authorization in ash-project ash_sql

The vulnerability arises because ash_sql's AggregateQuery.add_single_aggs/5 function rebuilds the outer query using only the {table, schema} tuple from query.from.source, omitting the tenant schema prefix stored in query.prefix or query.from.prefix. In multitenant applications using strategy(:context), this causes the rebuilt outer query to default to the repository's default schema, while the inner correlated subquery still uses the correct tenant schema. The join between these queries is only on the primary key, leading to aggregates and relationship joins being computed against data from the wrong tenant. This affects ash_sql versions >=0.1.0 and <0.7.1.

An attacker or caller in a multitenant environment can obtain aggregate data from another tenant's rows, potentially exposing sensitive information across tenant boundaries. The impact is limited to aggregate values and does not include direct data modification or broader access. The CVSS 4.0 base score is 2.1, indicating low severity.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. There is no official fix or patch link provided at this time. Users of affected versions should monitor vendor communications for updates and consider mitigating by restricting access or avoiding use of aggregate queries in multitenant contexts until a fix is available.