In PowerSync Service version 1.20.0, the sync engine incorrectly ignores certain subquery filters when a sync stream is configured with config.edition:3. This flaw allows an authenticated user to receive data that should have been excluded by those filters, effectively bypassing intended data access controls. The consequence is that sensitive data can be exposed to unintended users, violating confidentiality.

Affected components include @powersync:service-core, @powersync:service-sync-rules, and powersync-ja:powersync-service. The vulnerability exists only in version 1.20.0 and is fixed in 1.20.1. No other versions were reported to be affected.

The CVSS base score is 6.5, indicating a medium severity vulnerability that directly impacts the confidentiality of user data. EPSS indicates a very low exploitation probability (<1%). The flaw is not listed in CISA's KEV catalog and no specific exploitation tools are publicly known. The most likely attack vector requires the attacker to have legitimate credentials and to configure or modify a sync stream with config.edition:3 that includes unpartitioned subqueries. Once the vector is enabled, the attacker can trigger the sync and retrieve data beyond their authorized scope.