---
id: "CVE-2026-96581"
kind: "vulnerability"
aliases: ["CVE-2026-96581"]
title: "Ash: upsert lets one tenant read and take over another tenant's records"
severity: "high"
cvss: 7.6
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["ash", "elixir", "multitenancy", "package", "phoenix"]
not_affected_if: ["ash-below-1.22.0-or-3.37.2-plus", "no-attribute-multitenancy", "no-upsert-on-primary-key"]
published_at: "2026-10-26T08:17:20+00:00"
first_seen_at: "2026-10-26T08:28:59+00:00"
updated_at: "2026-10-26T08:30:20+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-96581", "first_seen_at": "2026-10-26T08:28:59+00:00"}]
---

# Ash: upsert lets one tenant read and take over another tenant's records

Ash, an Elixir framework, skips tenant scoping when an upserting create action matches an existing primary key. A user of one tenant who supplies another tenant's record id can read all of that record's attributes and move it into their own tenant.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `mix deps | grep ash` (or check `mix.lock`) to see the installed `ash` version
- Search the code for create actions with `upsert? true` that accept the primary key under multitenancy (attribute strategy)

## Fix

- Upgrade the `ash` package to `3.37.2` or later

## Timeline

- 2026-10-26T08:28:59+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-96581

## From the sources

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.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_