CVE-2026-30870

Affected queries

Subqueries used only to determine whether or not a table should be synced (without partitioning the data itself) are affected. Examples:

-- Goal: Sync a table only to admin users
-- 1.20.0: all authenticated users would sync this table
SELECT * FROM sensitive_table WHERE auth.user_id() IN (SELECT user_id FROM admins)
SELECT * FROM sensitive_table WHERE 1 IN (SELECT 1 FROM users WHERE id = auth.user_id() AND is_admin = TRUE)

-- Goal: Sync a table only if authorized
-- 1.20.0: all authenticated users would sync this table
SELECT * FROM sensitive_table WHERE 'sensitive_table' IN (SELECT table_name FROM synced_table WHERE "user" = auth.user_id())
SELECT * FROM sensitive_table WHERE 'sensitive_table' IN auth.parameter('allowed_tables')

Queries that partition data (for example SELECT * FROM sensitive_table WHERE owner IN (SELECT id FROM users WHERE is_admin AND id = auth.user_id())) are not affected by this issue.

In version 1.20.0, when using new sync streams with config.edition: 3, certain subquery filters were ignored when determining which data to sync to users.

Depending on the sync stream configuration, this could result in authenticated users syncing data that should have been restricted.

Only queries that gate synchronization using subqueries without partitioning the result set are affected.

Not affected:

• Sync rules (bucket_definitions)
• Sync streams using config.edition: 2
• No data is exposed without authenticating

CVE-2026-30870 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.20.1, 0.33.0); upgrading removes the vulnerable code path.

Kodem intelligence

The issue is fixed in 1.20.1. Restarting the service with the new version is sufficient - no reprocessing of sync streams is required.

Any data that users erroneously synced will be automatically removed from those devices when they connect again.

We have updated all affected PowerSync Cloud instances to the fixed version, and are reaching out to affected customers.

For self-hosted PowerSync instances, update to the latest version and restart.

1. What is CVE-2026-30870? CVE-2026-30870 is a medium-severity security vulnerability in @powersync/service-core (npm), affecting versions = 1.20.0. It is fixed in 1.20.1, 0.33.0.
2. How severe is CVE-2026-30870? CVE-2026-30870 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2026-30870?
   • @powersync/service-core (npm) (versions = 1.20.0)
   • @powersync/service-sync-rules (npm) (versions = 0.32.0)
4. Is there a fix for CVE-2026-30870? Yes. CVE-2026-30870 is fixed in 1.20.1, 0.33.0. Upgrade to this version or later.
5. Is CVE-2026-30870 exploitable, and should I be worried? Whether CVE-2026-30870 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-30870 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-30870?
   • Upgrade @powersync/service-core to 1.20.1 or later
   • Upgrade @powersync/service-sync-rules to 0.33.0 or later