# CVE-2026-78699: rename_tenant returns :ok on a failed rename, enabling cross-tenant access in AshPostgres

> Attackers can rename tenants to collide with existing schemas, gaining unauthorized read and write access to other tenants' data due to unchecked return values.

- **Severity:** High 7.2 (`CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 30 Aug 2026
- **Updated:** 1 Sep 2026
- **Also known as:** EEF-CVE-2026-78699, GHSA-6fqq-j9c4-5766

## What is CVE-2026-78699?

CVE-2026-78699 is a high-severity vulnerability in ash-project ash_postgres, published on 30 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Unchecked Return Value vulnerability in ash-project ash_postgres allows a user who can drive a tenant rename to a name that collides with an existing tenant's schema to have their tenant record repointed at that other tenant's live schema, gaining access to its data.

AshPostgres.MultiTenancy.rename_tenant/3 issues the ALTER SCHEMA ... RENAME TO ... with the non-raising Ecto.Adapters.SQL.query/2, discards its {:ok, _} | {:error, _} result, and unconditionally returns :ok. PostgreSQL rejects the rename when the target schema already exists (and on insufficient privilege or lock timeout), but that failure never reaches the caller. The calling manage_tenant update action therefore sees success and commits the tenant row with the new name, which is the schema of a different existing tenant, so subsequent reads and writes for that tenant run against the other tenant's data.

This issue affects ash_postgres: from 0.25.0 before 2.13.0.

Weakness: CWE-252 (Unchecked Return Value)

## Which versions are affected by CVE-2026-78699?

1 open source package ship an affected version, including ash_postgres.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `ash_postgres` | Hex | From 0.25.0 | 2.13.0 |

## How do I fix CVE-2026-78699?

Upgrade ash_postgres to 2.13.0 or later.

## Is CVE-2026-78699 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-78699 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-78699 and fix it if it is affected.

What it is: CVE-2026-78699 is a high-severity vulnerability in ash-project ash_postgres, published on 30 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-78699 exists.

Affected packages and fixed versions:
- ash_postgres (Hex): affected from 0.25.0; fixed in 2.13.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-78699/ (Markdown: https://insights.sbomify.com/CVE-2026-78699/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-78699
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-78699
- OSV: https://osv.dev/vulnerability/CVE-2026-78699

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-78699/
Summaries are generated and may contain mistakes; the official description above is the record.