CVE-2026-96581: An upsert on the primary key in Ash ignores attribute multitenancy, so one tenant can read, overwrite and take over another tenant's records

Severity: high (CVSS 7.6 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-26 · updated 2026-10-26
Weakness: CWE-639

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.

Affected products

ash-project ash: from 1.22.0 before 3.37.2 — fixed in 3.37.2

How to fix

Upgrade to a fixed version: ash-project ash 3.37.2. Check the vendor advisory for mitigations.

References

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