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CVE-2026-96581high7.6

An upsert on the primary key in Ash ignores attribute multitenancy, so one tenant can read, overwrite and take over another tenant's records

Impact

Authorization Bypass Through User-Controlled Key vulnerability in ash-project ash allows a user of one tenant to read, overwrite and take over another tenant's records via an upserting create action.

Source excerpt · EEF

What to do

Add upsert_condition expr(<tenant attribute> == ^tenant()) to every create action that upserts on the primary key or on an all_tenants? identity, and do not combine it with return_skipped_upsert?. An upsert into another tenant's record then fails with Ash.Error.Changes.StaleRecord (or is skipped in a bulk create) and leaves that record unchanged. This does not help on the Mnesia data layer, which ignores upsert conditions in affected versions.

EEF guidance

Affected packages

This source has no supported package-version data for matching. You can read the advisory here, but this record alone cannot power a dependency check.

Affected products

Vendor version evidence. Product records are separate from automatic dependency matching.

ash-project · ash

Other versions: unaffected

Version / rangeSource status
1.22.0 to before 3.37.2affected
EEF version evidence

ash-project · ash

Other versions: unaffected

Version / rangeSource status
2333d01ddf37e5909769a513059b27e3183331c5 to before c9f0cdb31e7c084def05f3f5be69dd7bb7721754affected
EEF version evidence

Original source description

Authorization Bypass Through User-Controlled Key vulnerability in ash-project ash allows a user of one tenant to read, overwrite and take over another tenant's records via an upserting create action.

Under attribute multitenancy, Ash.Actions.Create (lib/ash/actions/create/create.ex) and Ash.Actions.Create.Bulk (lib/ash/actions/create/bulk.ex) upserted on the primary key, or on an all_tenants? identity, without scoping the conflicting record to the request's tenant. A caller of a create action with upsert? true that accepts the primary key, supplying a record id from another tenant, updated that record's upsert fields and received all of its attributes in the result. With the default upsert fields the tenant attribute was written too, moving the record into the caller's tenant. Read and update policies do not run for upserts, and tenant-scoped create policies pass because the tenant is the caller's own.

This issue affects ash: from 1.22.0 before 3.37.2.

References