CVE-2026-81318: Distinct-query aggregate drops the tenant schema prefix, leaking across tenants in AshSql

Severity: low (CVSS 2.1 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-30 · updated 2026-09-01
Weakness: CWE-863

Description

Incorrect Authorization vulnerability in ash-project ash_sql allows a caller in a schema-based multitenant application to receive aggregate values computed from another tenant's rows. When an aggregate is computed over a distinct query, AshSql.AggregateQuery.add_single_aggs/5 rebuilds the outer query from query.from.source alone, which is only the {table, schema} tuple and does not carry query.prefix or query.from.prefix. For strategy(:context) multitenancy those hold the tenant schema, so the rebuilt outer query reads the repo's default schema while the inner correlated subquery still reads the tenant schema, and the two are joined only on primary key. The aggregate, and any relationship join added off the prefix-less binding, is then computed against the wrong tenant's rows. The neighbouring limit and exists branches instead wrap the query with subquery/1, which preserves the prefix. This issue affects ash_sql: from 0.1.0 before 0.7.1.

Affected products

ash-project ash_sql: from 0.1.0 before 0.7.1 — fixed in 0.7.1

How to fix

Upgrade to a fixed version: ash-project ash_sql 0.7.1. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-81318 or the next vulnerability affects your stack